Products of the Propargyl Self-Reaction at High Temperatures

Subscriber access provided by University of Otago Library

Article

Products of the Propargyl Self-Reaction at High Temperatures Investigated by IR/UV Ion Dip Spectroscopy Philipp Constantinidis, Florian Hirsch, Ingo Fischer, Arghya Dey, and Anouk M. Rijs J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b08750 • Publication Date (Web): 08 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

2nd revised version, Dec. 8th, 2016

Products of the Propargyl Self-Reaction at High Temperatures Investigated by IR/UV Ion Dip Spectroscopy

P. Constantinidis,a) F. Hirsch, a) I. Fischer,* a) A. Dey, b) A. M. Rijsb)

a) Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany, phone: +49-931/31-86360 b) Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, the Netherlands, phone: +31-24/3653940

E-mail:

[email protected]

[email protected]

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to)

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT The propargyl radical is considered to be of key importance in the formation of the first aromatic ring in combustion processes. Here we study the bimolecular (self-) reactions of propargyl in a high-temperature pyrolysis flow reactor. The aromatic reaction products are identified by IR/UV ion dip spectroscopy, using the free electron laser FELIX as mid-infrared source. This technique combines mass selectivity with structural sensitivity. We identified several aromatic reaction products based on their infrared spectra, among them benzene, naphthalene, phenanthrene, indene, biphenyl and surprisingly a number of aromatic compounds with acetylenic (ethynyl) side chains. The observation of benzene confirms that propargyl is involved in the formation of the first aromatic ring. The observation of compounds with acetylenic side chains shows that in addition to a propargyl- and phenylbased mechanism the HACA (hydrogen abstraction C2H2 addition) mechanism of polycyclic aromatic hydrocarbons formation is present, although no acetylene was used as a reactant. Based on the experimental results we suggest a mechanism that connects the two pathways.


Page 2 of 45

Page 3 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION

The objective of the present work is to investigate the role of propargyl radicals in the formation of PAH (polycyclic aromatic hydrocarbons) beyond the first ring by identifying the reaction products formed inside a pyrolysis micro-reactor. Small resonance-stabilized hydrocarbon radicals1 (RSRs) such as the C3H3 isomer propargyl, H-C≡C-CH2 play an important role in PAH growth in combustion processes.2 RSRs can accumulate in flames and contribute to molecular growth, because their reactivity towards O2 is lower than for their non-stabilized counterparts.3 In particular the recombination of propargyl is assumed to be the main route to the formation of the first aromatic ring, i.e. phenyl or benzene, which is considered to be a rate-determining step in PAH growth.2 Therefore considerable computational and experimental studies are dedicated to unravel its chemistry. At high temperature propargyl can be formed by hydrogen abstraction of allene and propyne as shown in shock tube studies4-7 or by the insertion reaction of methylene into acetylene.2,8-10 It also appears as a decomposition product in the pyrolysis of biomass.11-13 Recently, the stepwise addition of acetylene to propargyl was found to constitute a pathway to indene.14 Unimolecular dissociation reactions of propargyl were investigated in the laboratory using photoexcitation.15-19

PAH growth is mostly explained by the HACA (hydrogen abstraction C2H2 addition) mechanism, in which acetylene adds step-wise to an aromatic hydrocarbon radical.20 As it was found that HACA is too slow to account for the formation of large PAHs, alternative pathways like PAC21 (phenyl addition cyclization) and odd-carbon-pathways involving methyl22 or cyclopentadienyl23 were suggested. Given the importance of propargyl in combustion, it might also participate in the growth processes to larger PAHs via a C33 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

pathway. Studies on the recombination of propargyl are numerous, but they focus mostly on the understanding of benzene (C6H6) formation.24-28 At low temperatures recombination of C3H3 primarily leads to linear addition products, while at high temperatures and pressures isomerization to benzene and fulvene dominates.27,29 In addition the reaction to phenyl, 2 C3H3 → C6H5 + H is relevant, but seems to be less important than benzene formation.26 The consecutive step in a C3 pathway, the reaction of phenyl/benzene with a further propargyl radical, could lead to another RSR, phenylpropargyl (C9H7), which was only recently characterized spectroscopically.30-32 Previous IR/UV studies showed that it dimerizes to pterphenyl and 1-(phenylethynyl)naphthalene (1-PEN).33 Furthermore phenylacetylene (C8H6) and phenylpropyne (C9H8) have been found as products of the propargyl self-reaction,29 but higher masses have not yet been reported. Here we apply IR/UV ion dip spectroscopy34 to identify the aromatic products of the propargyl self-reaction in a pyrolysis tube.35 The interest in high temperature reactions36 triggered a number of studies on the chemistry occurring in such a reactor.11,13,33,37,38 Often photoionization using synchrotron radiation has been applied and products have been identified by their ionization energy.37,39-41 In the Discussion section below we will compare methods applied to identify products in high temperature reactions in more detail. Here we simply like to point out that combining the mass-selectivity of UV photoionization with the structural sensitivity of IR spectroscopy permits an identification of PAH product isomers33,38 and thus complements photoionization mass spectrometry in the identification of larger PAH.

EXPERIMENTAL Experiments were conducted in a differentially pumped molecular beam apparatus.34,42 High temperature reactions were carried out by flash pyrolysis in a resistively heated SiC tube (micro-reactor), mounted onto a pulsed solenoid valve. Propargyl bromide (stabilized with MgO, TCI Deutschland GmbH, purity > 97.0 %) kept at room temperature was used as 4 ACS Paragon Plus Environment

Page 4 of 45

Page 5 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


precursor for propargyl radical generation and seeded in 1.0 bar of argon. Note that the absence of toluene (which is often added as a stabilizer) was verified by NMR spectroscopy (Figure S1).

Pyrolysis conditions were chosen to maximize bimolecular reactions. The most important parameters are the radical number density that can be influenced via the temperature of the sample container, the pyrolysis temperature and the delay between laser and gas pulse. Early in the gas pulse there are few bimolecular reactions and cold propargyl radicals can be studied, while in the center of the gas pulse bimolecular reactions become relevant. All parameters were systematically varied and reaction conditions were optimized with the aid of photoionization mass spectrometry, using 118 nm radiation (Nd:YAG 9th harmonic) produced in a xenon gas cell. The pyrolysis tube was heated to around 1000 °C in the experiments described below as measured by a Type C thermocouple on the outside wall of the reactor, but there will be a radial temperature gradient inside the reactor. The pressure on the other hand will slightly decrease along the tube axis and sharply drop at the tube exit. Its variation inside the tube has been simulated for continuous operation.36 It is not well characterized for pulsed operation, but estimated to be on the order of several hundred mbar

IR/UV ion dip spectroscopy was carried out at the FELIX free electron laser laboratory43 (Radboud University, Nijmegen, the Netherlands). In this experiment the free jet is crossed by both FEL-IR and UV laser radiation. Molecules are ionized by the UV laser in a [1+1] process at a fixed wavelength. The IR laser is fired about 200 ns before the UV laser. When an IR active mode of the molecules is excited, a decrease of the UV laser ion signal (dip) is observed, because the molecular ground state is depopulated. Pulsed UV radiation (≈ 1 mJ) with a repetition rate of 10 Hz was provided by a frequency-doubled dye laser, pumped by a Nd:YAG laser and operating at wavelengths of 263 nm, 270 nm or 275.3 nm. The IR laser 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

was triggered at 5 Hz and scanned over the fingerprint region (550-1750 cm-1) at a step width of 2.5 cm-1. The signal was obtained by dividing the UV only signal (I0) by the IR+UV signal (I), taking the decadic logarithm and correcting for IR laser power.The final IR spectra were obtained after composing and averaging the experimental data at each single UV wavelength. In certain cases spectra of multiple wavelengths were averaged, which is indicated in the figures as sum of wavelengths (e.g. “263 + 275.3 nm”). Savitzky–Golay-Filtering was applied to improve the quality of the spectra. Most carriers were identified with the aid of frequency calculations, conducted at the DFT/B3LYP/6-311G(p,d) level of theory, employing the Gaussian09 computational chemistry software.44 The computed wavenumbers were scaled with a factor of 0.975 and convolved with a Lorentzian function with a full width at halfmaximum (fwhm) of 10 cm-1. For several molecules gas-phase FT-IR spectra were recorded to substantiate the assignment. These measurements were performed in a high-temperature gas cell specifically designed to investigate molecules with low vapor pressure, incorporated into a Bruker IFS120HR spectrometer.45

RESULTS


Page 6 of 45

Page 7 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a) Mass Spectra

Figure 1. Single photon ionization (SPI) mass spectrum (upper trace) and [1+1] resonance enhanced multiphoton ionization (REMPI) mass spectrum (lower trace) of the reaction products of the propargyl self-reaction. The spectra were recorded under similar conditions in the pyrolysis reactor. Figure 1 shows the photoionization mass spectra of the pyrolysis products of propargyl bromide. They were recorded at a pyrolysis temperature of around 1000 °C, which was sufficient to fully convert the precursor. The upper trace was recorded by VUV radiation of 118 nm (10.5 eV), which ionizes most molecules in the beam in a single photon process. While molecular ionization cross sections σion vary strongly around threshold, they become more similar at higher energies and the value of σion around 1 eV above threshold often approaches 10 Mb.46,47 The signal size in the 118 nm mass spectrum thus approximates the relative concentration of species reasonably well. Mass spectra as a function of the pyrolysis temperature are given in Figure S2 in the supporting information (SI), showing the development of the relative peak intensities with temperature. Beside the propargyl peak at 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

m/z = 39 (C3H3) a group of intense features appears in the spectrum at m/z = 78 (C6H6), 77 (phenyl) 76 (C6H4, possibly ortho-benzyne) and 74 (C6H2) and corresponds to products of propargyl dimerization followed by H- or H2 loss. Phenyl and ortho-benzyne are important reactants for subsequent PAH forming reactions. Peaks at m/z = 115 and 152 indicate that products with three and four C3-units are formed in the reactor. Unimolecular decomposition of propargyl to C3H2 and H leads to minor C3H2 concentrations and is considered less relevant for the formation of higher masses.26 A particularly interesting reaction product is C4H2 (m/z = 50), which is attributed to diacetylene. It is most likely produced by decomposition of a larger species. Dissociative photoionisation (DPI) is unlikely because of the narrow peak width and the fact that C4H2+ has not been observed as a DPI product in previous synchrotron radiation studies of important larger species, like o-benzyne (here C4H2 is generated at high temperatures by pyrolysis) or phenylpropargyl. Below we will argue that it originates from the thermal decomposition of C6H4. Note that species originating from dissociative ionization will exhibit the IR-spectrum of the parent molecule and can thus often be identified. Acetylene itself cannot be observed by 118 nm photoionization due to its high ionization energy of 11.40 eV.48 Two equally intense peaks at m/z = 156, 158 might be due to C6H5Br, possibly formed from a reaction of propargyl with the precursor propargyl bromide (C3H3Br). Some of the masses have been observed before by Jochnowitz et al.49, who operated a SiC microreactor under similar conditions. One should note, however that in addition to C3H3 a bromine atom is formed in the pyrolysis, which can abstract hydrogen atoms from propargyl, the most abundant reactive molecule in the beam, and form HBr and C3H2. HBr cannot be detected due to its high IE of 11.68 eV. 50

In the lower trace several of the small mass peaks are absent, because two-photon ionization requires an ionization energy (IE) below 9.43 eV. Several other smaller molecules, like 8 ACS Paragon Plus Environment

Page 8 of 45

Page 9 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


propargyl possess no excited states around 263 nm. Thus the spectrum does not represent the relative concentration of the pyrolysis products. On the other hand many higher mass peaks get more prominent in the 263 nm spectrum because intermediate electronic states resonantly enhance the ionization probability of almost all polycyclic aromatic molecules. While in the 118 nm mass spectrum growth by adding of C3 units is prominent, in the 263 nm spectrum spacings of 24/26 or 50 amu between the mass peaks are present, already indicating an additional growth mechanism by C2 or C4 units.

b) IR/UV Spectra For many of the larger molecules that appear in the mass spectra, the chemical structure cannot be inferred from simple mechanistic pictures, because too many isomers exist. We therefore apply IR/UV ion dip spectroscopy in combination with quantum chemical calculations of vibrational spectra to identify aromatic pyrolysis products. When calculations did not yield satisfactory agreement, FT-IR spectra of relevant molecules were recorded in a high-temperature gas cell. The UV wavelength employed for a given spectrum is indicated in the figure.

In the next sections the most important IR/UV spectra are shown. Before the assignments are discussed in detail, we would like to point out that the vast majority of closed-shell aromatic molecules possess electronically excited states in the range between 263 nm and 275 nm, see for example Ref.

51

. Although these resonances are typically broad, they can be resonantly

excited in a [1+1] REMPI (resonance enhanced MPI) process. As previously discussed in numerous publications, it is not necessary to excite a narrow electronic transition to observe an IR-UV ion dip signal.

52-55

This is due to the fact that either there are large increases in

absorption strength or large shifts in the REMPI spectrum. Additionally multiple photon 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

processes contribute to the signal because of the high IR intensity and the long pulse length of the FEL pulse allows the absorption of a second photon after vibrational relaxation.55 Nevertheless absorption of the first IR photon constitutes the bottleneck for the process, so IR spectra of the ground state are observed. It is only possible to record an IR spectrum that exhibits a resonant intermediate electronic excited state at the selected UV range using IR-UV ion dip spectroscopy, therefore no spectrum was recorded for propargyl itself. However, its formation in the pyrolysis has been verified in recent experiments using synchrotron radiation.56 In addition the signal also depends on the IR cross section and will be weak for modes with a small change in dipole moment. Thus for m/z = 115 we also did not succeed in recording IR/UV spectra of sufficient signal/noise (S/N) ratio. In a previous study, using a phenylpropargyl precursor as the starting material, IR spectra of moderate S/N ratio were recorded,33 but in the present experiments the concentration of phenylpropargyl was most likely too small given the low IR cross section.

Benzene and Simple Polycyclic Hydrocarbons

Figure 2. The IR/UV spectrum of m/z = 78 (upper trace) appears as a gain spectrum (upside down) and was assigned to benzene by comparison with a laboratory spectrum (lower trace).


Page 10 of 45

Page 11 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2 shows the IR/UV spectrum of m/z = 78. Since only a weak ion signal is visible in the two-photon mass spectrum at m/z = 78, a subsequently low signal/noise (S/N) ratio is observed in the IR/UV spectrum (see upper trace of Figure 2). Benzene is the most likely carrier of this peak, by comparison with a reference gas-phase IR spectrum. The IR/UV spectrum appears here inverted, as the ion signal increases (gain) when IR radiation is present. We therefore encounter a “hole filling” rather than a “hole burning” process.57 Vibrational excitation in the ground state seems to increase the photoionization cross section, probably because the S1 ← S0 transition is formally symmetry-forbidden and only allowed by vibronic coupling. A comparison of the IR/UV spectrum with computations for benzene and other important C6H6 isomers is given in Figure S3. The observation of benzene agrees with theory, which suggests that the recombination of two propargyl radicals leads via several linear C6H6 intermediates to the thermodynamically stable cyclic isomer benzene.24,25,28,58 However, many relevant (in particular open chain) isomers, like the primary dimerization product 1,5hexadiyne cannot be detected in our experiment, because they do not absorb between 260 nm and 275 nm. Thus no information on the relative importance of the various isomers can be derived.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 45

Figure 3. Naphthalene is the sole product with m/z = 128.

The first polycyclic molecule, naphthalene (C10H8) was readily identified by its characteristic band around 780 cm-1 in the IR/UV spectrum shown in Figure 3. Several routes have been proposed for the formation of naphthalene, for example step-wise addition of two acetyleneunits to phenyl, followed by H-atom loss.39 Alternatively a pathway (1) starting from two phenyl units has been computed,59 according to the reaction 2 C6H5 → C10H8 + C2H2

∆HR = -289 kJ⋅mol-1

(1)

Note that acetylene is formed as the second product and can be consumed in further reactions.

Figure 4. Biphenyl was identified by its computational spectrum. The band at 900 cm-1 indicates the possible presence of a second isomer.

Mass m/z = 154 was identified as biphenyl (Figure 4), a molecule that contains four C3 units. It has already been observed as the main reaction product in the self-reaction of phenyl radicals in a previous study.38 Therefore its appearance in the present experiment is not 12 ACS Paragon Plus Environment

Page 13 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surprising and regarded as a consequence of phenyl/benzene formation from propargyl. Several possible pathways for the reaction have been computed.59 Beside the phenyl recombination, the reaction of phenyl + benzene (2) and the disproportionation of benzene and triplet ortho-benzyne (3) are relevant: C6H6 + C6H5 → C12H10 + H

∆RH= -42 kJ⋅mol-1

(2)

C6H6 + o-C6H4 (triplet) → C12H10

∆RH= -503 kJ⋅mol-1

(3)

In the spectrum given in Figure 4 a prominent band is present at ≈ 900 cm-1 that is neither described by the computations nor was observed in an earlier experiment.38 A likely carrier is 2-ethenylnaphthalene (Figure S4).

Figure 5. The IR/UV spectrum of m/z = 178 is assigned to phenanthrene.

The peak at m/z = 178 was assigned to phenanthrene (Figure 5). Clearly, the computed spectrum of this isomer matches the experimental spectrum much better than other relevant isomers (Figure S5). Phenanthrene appears in flames in significantly higher amounts than anthracene.60,61 The reason for the selectivity of its formation is not easily understood within the HACA model. It was explained by the contribution of a reaction path proceeding via 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

acenaphthylene.62 In a recent study, Parker et al. however asserted that phenanthrene is not formed via such a two-step HACA reaction, originating from naphthalene.63 Formally the formation of phenanthrene could also follow from the reaction of acetylene with biphenyl.

Figure 6. Benzo[a]anthracene was assigned by its computational spectrum.

Mass m/z = 228 has been prominently observed in previous experiments on phenyl and phenylpropargyl. Since the mass corresponds to C18 hydrocarbons, its appearance can be expected within a mechanism based on C3 or C6 addition. Phenylpropargyl dimerization leads to 1-(phenylethynyl)naphthalene (1-PEN),33 while the self-reaction of phenyl yielded most likely triphenylene.38 Mass 228 was also observed in a fuel-rich premixed toluene flame.64 In our present study we again observe a peak at m/z = 228 (Figure 1, lower trace), which we assign to benzo[a]anthracene (Figure 6). A comparison with computed IR spectra of other isomers is given in Figure S6. Thus although each of the radicals investigated so far produces selectively a hydrocarbon of mass 228, it is always a different isomer, indicating that the reaction is kinetically controlled and not thermodynamically. Triphenylene as the suggested product of the PAC mechanism21 can be ruled out as well as 1-PEN. This indicates that the 14 ACS Paragon Plus Environment

Page 14 of 45

Page 15 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


m/z=228 product is not formed by condensation of phenyl units, but rather by sequential addition of C3 units.

Figure 7. The spectrum at m/z = 116 is probably best represented by a mixture of indene and 1-phenylpropyne.

The 600-850 cm-1 region of the IR/UV spectrum of m/z = 116 in the top trace of Figure 7 shows typical features of indene, a common product in high-temperature reactions.40 However, the bands between 1400 cm-1 and 1600 cm-1 are neither well represented by the computed spectrum (Figure S7) nor by the FT-IR reference spectrum given in the center trace of Figure 7. The IR/UV spectrum seems to contain the contribution of a further isomer, most likely 1-phenylpropyne. Further isomers do not contribute significantly, as can be concluded from Figure S7. Indene constitutes the most stable isomer on the C9H8 potential energy surface and can be formed by several routes. Under our experimental conditions the reaction of a C6-unit (benzene, phenyl or o-benzyne) with propargyl will dominate.65,66 In particular 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 45

the phenyl + propargyl radical/radical reaction, which proceeds via a phenylpropargyl intermediate is highly exothermic.50 C6H5 + C3H3 → C9H8 (indene)

∆HR = -517 kJ/mol

(4)

Starting from 1- and 3-phenylpropargyl radicals in a previous IR/UV study led to indene as the sole isomer of m/z = 116.33 A new pathway to indene was recently explored and involves consecutive addition of acetylene to propargyl.14 Matsugi et al. found that the reaction of obenzyne with propargyl leads to indenyl as the dominant product.66 Finally open-chain C9H8 isomers have been observed in a VUV photoionization study on the reaction of phenyl with propyne.40 1-Phenylpropyne was also suggested to be the main C9H8 product isomer in a GC/MS analysis of the propargyl radical self-reaction.29


Page 17 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Reaction products with ethynyl side chains

Figure 8. IR/UV spectra of reaction products with ethynyl side chains. Ethynyl compounds are identifiable by a pair of bands in the 600-680 cm-1 range (CH bending fundamentals) and an intense band around 1220 cm-1 (overtone/combination band). In addition to the polycyclic molecules discussed above, a number of further reaction products are visible in the MPI mass spectrum, for example m/z = 102, 126, 150, 152, 176, 200, 202, 226, 250, and higher masses. A spacing of 24 amu between peaks is striking and suggests a growth by addition of C2 (ethyne) units. Note that within the HACA mechanism the first step is hydrogen abstraction from an aromatic molecule and formation of a radical. This step is followed by addition of acetylene and finally loss of another H-atom. All the IR/UV spectra in Figure 8 exhibit a prominent band around 1220 cm-1 and a pair of equally intense bands in the 600-680 cm-1 range. 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 9. 1,4-diethynylbenzene was identified by its gas-phase FTIR spectrum. An anharmonic frequency computation illustrates the contribution of fundamental, overtone and combination bands.

In the case of the m/z=126 product, simple computations for possible carriers do not yield a match for the 1220 cm-1 band, while the peak is observed in the gas-phase FT-IR spectrum of 1,4-diethynylbenzene (center trace of Figure 9). This band is typical for terminal alkynes and is caused by overtones and/or combination bands of the acetylenic ≡CH bending mode.67,68 Figure 9 depicts the comparison between experiment and calculation for 1,4diethynylbenzene. To account for the overtone/combination band, we conducted anharmonic calculations, applying generalized 2nd order vibrational perturbation theory (GVPT2), as implemented in the Gaussian09 package.44 A good fit of the experimental spectrum was achieved using a hybrid scheme69, where anharmonic frequency computations on the (B3LYP/6-311g++(g,d)) level were combined with high level harmonic computations 18 ACS Paragon Plus Environment

Page 18 of 45

Page 19 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(B2PLYP/aug-cc-pVTZ). The various isomers of diethynylbenzene can be distinguished by the 830 cm-1 band, which is red-shifted in the 1,2- and 1.3-isomers and in phenyldiacetylene (Figure S8). Note that this comparison was based on harmonic calculations of the isomers. Although small contributions cannot be ruled out, the 1,4-isomer dominates the spectrum. The absence of the 1,2-isomer can either be explained by steric hindrance or by a Bergmann cyclization, which consumes this isomer by ultimately forming naphthalene.70

Proceeding in a similar fashion several of the other mass-selected spectra assembled in Figure 8 can be assigned. The spectrum of m/z = 102 is assigned to phenylacetylene (Figure S9). In general phenylacetylene is a typical product of the HACA mechanism and formed via C6H5 + C2H2 → C8H6 + H

(5)

Alternatively it can emerge from the reaction of o-benzyne (C6H4) with acetylene.71 One of the most interesting masses is m/z = 152, which has been observed before in a number of high temperature experiments. The reaction of 1-naphthyl and 2-naphthyl with acetylene was assumed to yield primarily acenaphthylene, beside 1- or 2-ethynylnaphthalene.63,72 It also appears as product of o-benzyne dimerization, where it was assumed to correspond to biphenylene.73 In contrast our IR/UV spectra provide compelling evidence for the presence of an alkynyl side chain in the compound. The best match is given by the 2-ethynylnaphthalene isomer, as demonstrated from a gas-phase IR-spectrum of the pure compound (Figure 10). Figure S10 shows the 1-ethynylnaphthalene isomer provides an inferior match, while acenaphthylene and biphenylene can be excluded as carriers of the spectrum. In our prior study on the self-reaction of phenyl radicals m/z = 152 could also not be attributed to either biphenylene and acenaphthylene.38 With the present information, we can now assign m/z=152 to an ethynyl compound. Interestingly recent computations suggested ethynylnaphtahelene to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

play an important role in PAH growth above 1000 K.62 The small naphthylethylene contribution visible in the IR spectrum of m/z = 154 (vide supra) might also be connected to 2-ethynylnaphthalene via a H2 addition or loss process.

Figure 10. M/z = 152 is assigned to 2-ethynylnaphthalene based on comparison with a gasphase IR spectrum (center trace) and computations (bottom trace).

Assignment of the higher masses becomes successively more difficult. For m/z = 150 the possible carriers are either 1,2,4-triethynylbenzene or (4-ethynylphenyl)diacetylene based on the absorption bands at 1480 cm-1 and 830 cm-1 (Figure S11). Mass 176 might originate from naphthalene substituted with one diacetylene group or two ethynyl groups, while m/z = 200 corresponds to addition of a third ethynyl group to a naphthyl radical (see Figure S12 for the IR/UV spectra) and m/z = 202 to a phenanthrenyl with one acetylene unit added (Figure S13). Due to the large numbers of possible isomers, we cannot assign the carriers unambiguously.


Page 20 of 45

Page 21 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


DISCUSSION Before we start to discuss the results we would like to compare IR/UV spectroscopy to other methods that have been applied to detect products of high-temperature reactions. Each method has its unique strengths and weaknesses: Haefliger and Zenobi51 applied [1+1] REMPI to the identification of PAH molecules and compared it to GC/MS. The disadvantages of the latter are the comparably large necessary sample amounts and the laborious sample preparation. Its advantage over the highly sensitive REMPI on the other hand is the availability of quantitative information. Furthermore REMPI relies on the existence of a UV chromophore. As an alternative VUV one-photon ionization is increasingly applied to detect products in pyrolysis tubes,39,40,63 chemical reactors74 or flames.75 It is not as sensitive as REMPI, but a fully universal detection scheme, because every molecule can be ionized. Sufficiently above the ionization threshold the ionization cross sections are similar enough to allow extracting relative concentrations. While isomer sensitivity has been accomplished for small molecules, it is on the other hand difficult to distinguish isomers of larger molecules, like PAH. Here photoelectron-photoion coincidence spectroscopy offers distinct advantages. It has been employed to monitor the chemistry inside a pyrolysis source,76,77 and recently been applied to flames78, but whether isomers of PAH can be distinguished remains to be seen. As an alternative IR/UV spectroscopy comes in. While not applicable to small molecules that cannot be electronically excited with common dye lasers, isomer-selective identification of aromatic molecules and PAH is straightforward. It thus offers unique benefits and supplements the methods mentioned above. In particular when the results are combined with those from onephoton ionization it constitutes a powerful and versatile approach. An example is the molecule with m/z=152 (see Figure 10), which is identified as 2-ethynylnaphthalene. Acenaphtylene and biphenylene can be ruled out, as can be seen in Figure S10.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The HACA mechanism, i.e. addition of acetylene to hydrocarbon radicals followed by Hatom loss is still considered to be the main path to PAHs, although computations suggest that it can only explain part of the PAH formation.62,79 Alternative models were developed, relying for example on reactions of phenyl radicals,21 which lead to polycyclic molecules in a few steps. Considering that C3H3 plays an important role in the formation of the first aromatic ring, one can assume C3-hydrocarbons to be also effective in PAH growth. While several computational studies investigated the reaction of C3H3 with o-benzyne66, phenyl, benzene65, benzyl66 and naphthyl or naphthalene80, which all lead to PAH molecules, there is a lack of experimental data that provide benchmarks for these computations. The aim of this study was to identify the most important product isomers and provide such a guideline. Computations will then help to extract mechanistic information on these reactions.

Scheme 1. The propargyl radical and the reaction products of its self-reaction identified by IR/UV ion dip spectroscopy (solid boxes). Small aliphatic hydrocarbons, phenyl and benzyne 22 ACS Paragon Plus Environment

Page 22 of 45

Page 23 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


have not been detected by IR/UV, but are supposed to participate in the growth process based on mass spectrometric detection (dashed box). Scheme 1 summarizes the identified reaction products. While the one-photon mass spectrum is dominated by groups of peaks separated by C3 units (m/z = 76/77/78, 115, 152/154, 190), the [1+1] two-photon mass spectrum shows series of peaks separated by C2-units (m/z = 102, 126, 128, 150, 152, 176, 178, 200, 202, 226, 228). The carriers were identified by IR/UV ion dip spectroscopy to be (1) o-fused 6-ring-PAHs like naphthalene and phenanthrene and (2) compounds with ethynyl (-C2H) side chains, which supports the presence of an acetylene addition pathway. Interestingly no cyclopenta-fused aromatic molecules were observed, which were considered to be markers for the HACA mechanism.70.

Benzene is the sole identifiable C6H6 isomer in our experiment, but as noted above isomers that do not absorb in the range between 260 nm and 275 nm like 1,5-hexadiyne will not be detected in the experiment. Phenyl (C6H5) and o-benzyne (C6H4) are formed by successive H or H2 loss and constitute important reactants in PAH growth, due to their high reactivity. The peaks at m/z = 74 (C6H2) and m/z = 98 (C8H2) indicate in addition the formation of polyynes. Biphenyl (m/z = 154) and benzo[a]anthracene (m/z = 228) originate from further condensation. Since the m/z=228 product observed here is different from the one found in the previous study on phenyl condensation (triphenylene),38 it is probably formed by successive addition of C3 species rather than a condensation of phenyl radicals (PAC-mechanism). Other products of the PAC mechanism such as terphenyls are not observed. To form even larger PAH during the 10-100 µs residence time in the reactor81 the concentration of propargyl and phenyl are not high enough.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 45

The first species beyond benzene in a possible C3 growth pathway is m/z = 115 (C9H7), which shows an intense ion signal in the one-photon mass spectrum (Figure 1). While in a former study the IR/UV spectra of 1- and 3-phenylpropargyl (m/z = 115) were recorded and assigned after selective generation from a bromide precursor,33 m/z = 115 could not be unambiguously identified here. The high reactivity and presumably short excited-state lifetimes make resonant ionization difficult. Yet the observation of indene (m/z = 116) is an indicator for the presence of C9H7 isomers in the pyrolysis. Dimerization products of phenylpropargyl have not been observed.

The large number of peaks separated by 24 amu in the [1+1] mass spectrum indicates the presence of an additional C2 growth process. The formation of several products with ethynyl side chains suggests reactions with acetylene in a HACA-type reaction. We want to emphasize that signal strength in [1+1] ionization depends strongly on the resonance enhancement, thus the ionization probability significantly increases for larger aromatic molecules, which all resonantly absorb at around 263 nm.51 The smaller molecules that dominate the 118 nm spectrum, like propargyl itself, possess no intermediate states in this wavelength that can be resonantly excited.

Since in contrast to earlier studies based on photoionization detection no acetylene was added to the reactant,39,63 the occurrence of these products is nevertheless surprising. Therefore, we considered alternative explanations for their appearance. For example, formation of phenylacetylene by a reaction of benzene (6) or phenyl (7) with propargyl, according to C6H6 + C3H3 → C8H6 + CH3

∆HR = +30 kJ/mol

(6)

C6H5 + C3H3 → C8H6 + CH2

∆HR = +15 kJ/mol

(7)

is endothermic and thus thermochemically unlikely (∆HR was calculated from ∆Hf values, obtained from Ref

50

). In addition no CH3 is observed in the 118 nm mass spectrum. For 24 ACS Paragon Plus Environment

Page 25 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


comparison, the formation of indene according to (4) is highly exothermic. Shafir et al. observed phenylacetylene in their propargyl study in a heated quartz reactor and explained it by a reaction of phenyl with propyne.29 However, in their experiments propyne was used as a propargyl precursor and thus present in considerable amounts. Other investigations of the C9H9, C9H8 65, C9H766 PES did not provide evidence for a fragmentation pathway leading to molecules with ethynyl side chains, nor did other computational studies of propargyl reactions.66,80 The challenge for the interpretation of the experimental results is therefore to identify a possible acetylene source that is responsible for the formation of HACA-type reaction products.

We suggest m/z = 76 (benzyne) as a possible acetylene source, because its high intensity in the mass spectrum is remarkable. Jochnowitz et al. observed C6H4 along with C6H6 in a similar reactor as soon as the reaction conditions were suitable for propargyl dimerization.49 In our experiments this mass seems to be associated with the formation of larger products, m/z = 115, 152 (76 + 39, 2 × 76). An explanation for its appearance could be H-loss from phenyl or H2-loss from benzene yielding o-benzyne. Both processes would carry away the excess energy available after propargyl dimerization. The reaction channel leading from propargyl directly to phenyl + H was considered less relevant in the temperature range of 1100 – 2100 K,26 but our experiments were conducted at the lower end of this range. In fact H-atom loss is the dominant decomposition pathway of phenyl radicals.59 A further route to C6H4 might proceed via propargylene, a possible propargyl dissociation product,82 because the dimerization of propargylene has been observed experimentally, the dimer probably being an open-chain

compound.83

Linear

C 6 H4

could

also

be

formed

directly

by

abstraction/elimination of linear C6H6, the initial reaction product of propargyl dimerization.


H


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Computational studies found two high temperature decomposition pathways for obenzyne:84,85 C6H4 → C4H2 + C2H2

(9)

C6H4 → C6H2 + H2

(10)

Reaction enthalpies, rate constants and branching ratios for (9) and (10) have been computed.85 Thus C6H4, which appears with significant intensity in the mass spectrum in Figure 1, constitutes an acetylene source via reaction (9). The second product, diacetylene, C4H2 could be involved in the addition of C4 units, an alternative pathway to some of the products observed. Furthermore the signal at m/z = 74 can be explained by reaction (10). Fragmentation of o-benzyne (and/or other C6 species) could thus provide the reactants for several of the observed reaction products. It would also link a pathway based on C3 or phenyl addition with the HACA mechanism. The hypothesis that C6H4 plays a central role will be tested in future experiments, exploring the bimolecular chemistry of o-benzyne in a chemical reactor.

SUMMARY AND CONCLUSION Products of the self-reaction of propargyl in a pyrolytic flow reactor were investigated in situ by IR/UV ion dip spectroscopy. This method combines the mass-selectivity of resonant photoionization with the structural sensitivity of IR spectroscopy and thus complements VUV-photoionization for establishing the chemical structure of aromatic reaction products. Benzene was observed, confirming the role of propargyl dimerization in the formation of the first aromatic ring. Beside PAH molecules like naphthalene and phenanthrene that are expected to form in a high temperature environment, two further classes of products were detected, (a) molecules whose formation can be described by the addition of C3 or C6 units 26 ACS Paragon Plus Environment

Page 26 of 45

Page 27 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and (b) molecules with ethynyl side chains which are expected to be formed in a HACA-like process. Indene, 1-phenylpropyne and biphenyl indicate the further participation of propargyl in the formation of hydrocarbons beyond benzene in a C3 growth pathway. Aromatic molecules with ethynyl side chains were identified by characteristic vibrational bands at around 1220 cm-1 and 600-680 cm-1 that are due to the acetylenic CH bending mode. The appearance of molecules with acetylenic side chains is surprising, because the experiments were performed using a clean propargyl bromide sample without any co-reagent. Their formation has not been detected before in the propargyl self-reaction. The 118 nm photoionization mass spectrum displays an intense peak at m/z = 76 that might be assigned to o-benzyne, thought to be a further product of propargyl dimerization. Decomposition of C6H4 to C4H2 + C2H2 is known to be a major decomposition pathway at elevated temperatures. Acetylene produced in this reaction can participate in PAH growth in the pyrolysis reactor. Our results thus suggest a close connection between a propargyl- and phenyl-based pathway and a HACA pathway to polycyclic aromatic hydrocarbons. Ortho-benzyne is a possible candidate for this connection. The hypothesis will be tested in an upcoming study on the selfreaction of o-benzyne.

ACKNOWLEDGEMNTS:

This work was supported by the German Science

Foundation, DFG through contract FI 575/8-2. Furthermore the research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312284. We gratefully thank the FELIX staff for their experimental support and we acknowledge the Stichting voor Fundamenteel Onderzoek der Materie (FOM) for the support of the FELIX laboratory (project no. N2300N).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

SUPPORTING INFORMATION PARAGRAPH A comparison of IR/UV spectra with additional computations, discussing alternative assignments, and full ref. 12 and 44 are given in the supporting information. This material is available free of charge via the Internet at http://pubs.acs.org.

REFERENCES

(1) Schmidt, T. W. The Electronic Spectroscopy of Resonance Stabilised Hydrocarbon Radicals. Int. Rev. Phys. Chem. 2016, 35, 209-242. (2) Miller, J. A.; Melius, C. F. Kinetic and Thermodynamic Issues in the Formation of Aromatic Compounds in Flames of Aliphatic Fuels. Combust. Flame 1992, 91, 21-39. (3) Hahn, D. K.; Klippenstein, S. J.; Miller, J. A. A Theoretical Analysis of the Reaction Between Propargyl and Molecular Oxygen. Faraday Discuss. 2002, 119, 79-100. (4) Lifshitz, A.; Frenklach, M.; Burcat, A. Pyrolysis of Allene and Propyne Behind Reflected Shocks. J. Phys. Chem. 1976, 80, 2437-2443. (5) Wu, C. H.; Kern, R. D. Shock-Tube Study of Allene Pyrolysis. J. Phys. Chem. 1987, 91, 6291-6296. (6) Bentz, T.; Giri, B. R.; Hippler, H.; Olzmann, M.; Striebel, F.; Szöri, M. Reaction of Hydrogen Atoms with Propyne at High Temperatures: An Experimental and Theoretical Study. J. Phys. Chem. A 2007, 111, 3812-3818. (7) Hidaka, Y.; Nakamura, T.; Miyauchi, A.; Shiraishi, T.; Kawano, H. Thermal Decomposition of Propyne and Allene in Shock Waves. Int. J. Chem. Kinet. 1989, 21, 643666. (8) Canosa-Mas, C. E.; Ellis, M.; Frey, H. M.; Walsh, R. The Formation of C3H3 (Propynyl) Radicals in the Reaction of CH2 (1A1) with Acetylene. Int. J. Chem. Kin. 1984, 16, 1103-1110. (9) Blitz, M. A.; Beasley, M. S.; Pilling, M. J.; Robertson, S. H. Formation of the Propargyl Radical in the Reaction of 1CH2 and C2H2: Experiment and Modelling. Phys. Chem. Chem. Phys. 2000, 2, 805-812. (10) Davis, F. H.; Shu, J.; Peterka, D. S.; Ahmed, M. Crossed Beams Study of the Reaction 1CH2+C2H2→C3H3+H. J. Chem. Phys. 2004, 121, 6254-6257. (11) Vasiliou, A.; Nimlos, M. R.; Daily, J. W.; Ellison, G. B. Thermal Decomposition of Furan Generates Propargyl Radicals. J. Phys. Chem. A 2009, 113, 85408547. (12) Vasiliou, A. K.; Kim, J. H.; Ormond, T. K.; Piech, K. M.; Urness, K. N.; Scheer, A. M.; Robichaud, D. J.; Mukarakate, C.; Nimlos, M. R.; Daily, J. W. et al, Biomass Pyrolysis: Thermal Decomposition Mechanisms of Furfural and Benzaldehyde. J Chem. Phys. 2013, 139, 104310. (13) Scheer, A. M.; Mukarakate, C.; Robichaud, D. J.; Ellison, G. B.; Nimlos, M. R. Radical Chemistry in the Thermal Decomposition of Anisole and Deuterated Anisoles: An Investigation of Aromatic Growth. J. Phys. Chem. A 2010, 114, 9043-9056. 28 ACS Paragon Plus Environment

Page 28 of 45

Page 29 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Savee, J. D.; Selby, T. M.; Welz, O.; Taatjes, C. A.; Osborn, D. L. Time- and Isomer-Resolved Measurements of Sequential Addition of Acetylene to the Propargyl Radical. J. Phys. Chem. Lett. 2015, 6, 4153-4158. (15) Deyerl, H.-J.; Fischer, I.; Chen, P. Photodissociation Dynamics of the Propargyl Radical. J. Chem. Phys. 1999, 111, 3441-3448. (16) Zierhut, M.; Noller, B.; Schultz, T.; Fischer, I. Excited-State Decay of Hydrocarbon Radicals, Investigated by Femtosecond Time-Resolved Photoionisation: Ethyl, Propargyl, and Benzyl. J. Chem. Phys. 2005, 122, 094302. (17) Schüßler, T.; Roth, W.; Gerber, T.; Fischer, I.; Alcaraz, C. The VUV Photochemistry of Radicals: C3H3 and C2H5. Phys. Chem. Chem. Phys. 2005, 7, 819-825. (18) Crider, P. E.; Castiglioni, L.; Kautzman, K. E.; Neumark, D. M. Photodissociation of the Propargyl and Propynyl (C3D3) Radicals at 248 and 193 nm. J. Chem. Phys. 2009, 130. (19) Goncher, S. J.; Moore, D. T.; Sveum, N. E.; Neumark, D. M. Photofragment Translational Spectroscopy of Propargyl Radicals at 248 nm. J. Chem. Phys. 2008, 128. (20) Frenklach, M.; Wang, H. Detailed Modeling of Soot Particle Nucleation and Growth. 23rd Symp. (Int.) Combustion 1991, 23, 1559-1566. (21) Shukla, B.; Koshi, M. A Highly Efficient Growth Mechanism of Polycyclic Aromatic Hydrocarbons. Phys. Chem. Chem. Phys. 2010, 12, 2427-2437. (22) Roesler, J. F.; Martinot, S.; McEnally, C. S.; Pfefferle, L. D.; Delfau, J. L.; Vovelle, C. Investigating the Role of Methane on the Growth of Aromatic Hydrocarbons and Soot in Fundamental Combustion Processes. Comb. Flame 2003, 134, 249-260. (23) Melius, C. F.; Colvin, M. E.; Marinov, N. M.; Pit, W. J.; Senkan, S. M. Reaction mechanisms in aromatic hydrocarbon formation involving the C5H5 cyclopentadienyl moiety. 26th Symp. (Int.) Combustion 1996, 685-692. (24) Alkemade, U.; Homann, K. H. Formation of C6H6 Isomers by Recombination of Propynyl in the System Sodium Vapour/Propynylhalide. Z. Phys. Chem. 1989, 161, 19. (25) Miller, J. A.; Klippenstein, S. J. The Recombination of Propargyl Radicals and Other Reactions on a C6H6 Potential. J. Phys. Chem. A 2003, 107, 7783-7799. (26) Scherer, S.; Just, T.; Frank, P. High-Temperature Investigations on Pyrolytic Reactions of Propargyl Radicals. Proc. Combust. Inst. 2000, 28, 1511-1518. (27) Tang, W.; Tranter, R. S.; Brezinsky, K. Isomeric Product Distributions from the Self-Reaction of Propargyl Radicals. J. Phys. Chem. A 2005, 109, 6056-6065. (28) Tang, W.; Tranter, R. S.; Brezinsky, K. An Optimized Semidetailed Submechanism of Benzene Formation from Propargyl Recombination. J. Phys. Chem. A 2006, 110, 2165-2175. (29) Shafir, E. V.; Slagle, I. R.; Knyazev, V. D. Kinetics and Products of the SelfReaction of Propargyl Radicals. J. Phys. Chem. A 2003, 107, 8893-8903. (30) Reilly, N. J.; Kokkin, D. L.; Nakajima, K.; Nauta, K.; Kable, S. H.; Schmidt, T. W. Spectroscopic Observation of the Resonance Stabilized 1-Phenylpropargyl Radical. J. Am. Chem. Soc. 2008, 130, 3137-3142. (31) Reilly, N. J.; Nakajima, M.; Gibson, B. A.; Schmidt, T. W.; Kable, S. H. LaserInduced Fluorescence and Dispersed Fluorescence Spectroscopy of Jet-Cooled 1Phenylpropargyl Radical J. Chem. Phys. 2009, 130, 144313. (32) Holzmeier, F.; Lang, M.; Hemberger, P.; Fischer, I. Improved Ionization Energies for the Two Isomers of Phenylpropargyl Radical. ChemPhysChem 2014, 15, 3489 – 3492. (33) Fischer, K. H.; Herterich, J.; Fischer, I.; Jaeqx, S.; Rijs, A. M. Phenylpropargyl Radicals and Their Dimerization Products: An IR/UV Double Resonance Study. The Journal of Physical Chemistry A 2012, 116, 8515-8522. 29 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(34) Rijs, A. M.; Oomens, J. Gas-Phase IR Spectroscopy and Structure of Biological Molecules. Topics in Current Chemistry 2015, 364, 1. (35) Kohn, D. W.; Clauberg, H.; Chen, P. Flash Pyrolysis Nozzle for Generation of Radicals in a Supersonic Jet Expansion. Rev. Sci. Instrum. 1992, 63, 4003-4005. (36) Guan, Q.; Urness, K. N.; Ormond, T. K.; David, D. E.; Barney Ellison, G.; Daily, J. W. The Properties of a Micro-Reactor for the Study of the Unimolecular Decomposition of Large Molecules. Int. Rev. Phys. Chem. 2014, 33, 447-487. (37) Custodis, V. B. F.; Hemberger, P.; Ma, Z.; van Bokhoven, J. A. Mechanism of Fast Pyrolysis of Lignin: Studying Model Compounds. J. Phys. Chem. B 2014, 118, 8524– 8531. (38) Constantinidis, P.; Schmitt, H. C.; Fischer, I.; Yan, B.; Rijs, A. M. Formation of Polycyclic Aromatic Hydrocarbons from Bimolecular Reactions of Phenyl Radicals at High Temperatures. Phys. Chem. Chem. Phys. 2015, 17, 29064-29071. (39) Parker, D. S. N.; Kaiser, R. I.; Troy, T. P.; Ahmed, M. Hydrogen Abstraction/Acetylene Addition Revealed. Angew. Chem. Int. Ed. 2014, 126, 7874-7878. (40) Zhang, F.; Kaiser, R. I.; Kislov, V. V.; Mebel, A. M.; Golan, A.; Ahmed, M. A VUV Photoionization Study of the Formation of the Indene Molecule and Its Isomers. J. Phys. Chem. Lett. 2011, 2, 1731-1735. (41) Lang, M.; Holzmeier, F.; Fischer, I.; Hemberger, P. Threshold Photoionization of Fluorenyl, Benzhydryl, Diphenylmethylene, and Their Dimers. J. Phys. Chem. A 2013, 117, 5260−5268. (42) Constantinidis, P.; Lang, M.; Herterich, J.; Fischer, I.; Auerswald, J.; Krueger, A. Electronic Spectroscopy of 1-(Phenylethynyl)naphthalene. J. Phys. Chem. A 2014, 118, 2915-2921. (43) Oepts, D.; van der Meer, A. F. G.; van Amersfoort, P. W. The Free-ElectronLaser user facility FELIX. Infrared Phys. Technol. 1995, 36, 297-308. (44) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al, Gaussian 09, Gaussian Inc.: Wallingford, CT, USA, 2009. (45) Herterich, J.; Zeißner, S.; Fischer, I. Gas-Phase IR and Solid-State Raman Investigation of Paracyclophanes. Z. Phys. Chem. 2013, 227, 23-34. (46) Cool, T. A.; Wang, J.; Nakajima, K.; Taatjes, C. A.; McIlroy, A. Photoionization Cross Sections for Reaction Intermediates in Hydrocarbon Combustions. Int. J. Mass. Spec. 2005, 247, 18-27. (47) Yang, B.; Wang, J.; Cool, T. A.; Hansen, N.; Skeen, S.; Osborn, D. L. Absolute Photoionization Cross-Sections of Some Combustion Intermediates. Int. J. Mass. Spec. 2012, 309, 118-128. (48) Bieri, G.; Burger, F.; Heilbronner, E.; Maier, J. P. Valence Ionization Energies of Hydrocarbons. Helv. Chim. Acta 1977, 60, 2213-2233. (49) Jochnowitz, E. B.; Zhang, X.; Nimlos, M. R.; Varner, M. E.; Stanton, J. F.; Ellison, G. B. Propargyl Radical: Ab Initio Anharmonic Modes and the Polarized Infrared Absorption Spectra of Matrix-Isolated HCCCH2. J. Phys. Chem. A 2005, 109, 3812-3821. (50) NIST Chemistry WebBook, NIST Standard Reference Database Number 69; Linstrom, P. J.; Mallard, W. G., Eds.; National Institute of Standards and Technology: Gaithersburg MD, 20899. http://webbook.nist.gov (retrieved July 20, 2016). (51) Haefliger, O. P.; Zenobi, R. Laser Mass Spectrometric Analysis of Polycyclic Aromatic Hydrocarbons with Wide Wavelength Range Laser Multiphoton Ionization Spectroscopy. Anal. Chem. 1998, 70, 2660-2665. (52) Rijs, A. M.; Sandig, N.; Blom, M. N.; Oomens, J.; Hannam, J. S.; Leigh, D. A.; Zerbetto, F.; Buma, W. J. Controlled Hydrogen-Bond Breaking in a Rotaxane by Discrete Solvation. Angew. Chem. Int. Ed. 2010, 49, 3896-3900. 30 ACS Paragon Plus Environment

Page 30 of 45

Page 31 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(53) Rijs, A. M.; Kabeláč, M.; Abo-Riziq, A.; Hobza, P.; de Vries, M. S. Isolated Gramicidin Peptides Probed by IR Spectroscopy. ChemPhysChem 2011, 12, 1816-1821 (54) Rijs, A. M.; Ohanessian, G.; Oomens, J.; Meijer, G.; von Helden, G.; Compagnon, I. Internal Proton Transfer Leads to Stable Zwitterionic Structures in a Neutral Isolated Peptide. Angew. Chem. Int. Ed. 2010, 49, 2332-2335. (55) Schmitt, M.; Spiering, F.; Zhaunerchyk, V.; Jongma, R. T.; Jaeqx, S.; Rijs, A. M.; van der Zande, W. J. Far-Infrared Spectra of the Tryptamine A Conformer by IR-UV Ion Gain Spectroscopy Phys. Chem. Chem. Phys. 2016, DOI: 10.1039/C6CP02358D (56) Hemberger, P.; Lang, M.; Noller, B.; Fischer, I.; Alcaraz, C.; Cunha de Miranda, B. K.; Garcia, G. A.; Soldi-Lose, H. Photoionization of Propargyl and Bromopropargyl Radicals: A Threshold Photoelectron Spectroscopic Study. J. Phys. Chem. A 2011, 115, 2225-2230. (57) Roithova, J. Characterization of Reaction Intermediates by Ion Spectroscopy. Chem. Soc. Rev. 2012, 41, 547-559. (58) Stein, S. E.; Walker, J. A.; Suryan, M. M.; Fahr, A. A New Path to Benzene in Flames. 23rd Symp. (Int.) Combust. 1991, 23, 85-90. (59) Comandini, A.; Brezinsky, K. Theoretical Study of the Formation of Naphthalene from the Radical/π-Bond Addition between Single-Ring Aromatic Hydrocarbons. J. Phys. Chem. A 2011, 115, 5547-5559. (60) Vincitore, A. M.; Senkan, S. M. Polycyclic Aromatic Hydrocarbon Formation in Opposed Flow Diffusion Flames of Ethane. Combust. Flame 1998, 114, 259-266. (61) Marinov, N. M.; Pitz, W. J.; Westbrook, C. K.; Vincitore, A. M.; Castaldi, M. J.; Senkan, S. M.; Melius, C. F. Aromatic and Polycyclic Aromatic Hydrocarbon Formation in a Laminar Premixed n-Butane Flame. Combust. Flame 1998, 114, 192-213. (62) Kislov, V. V.; Sadovnikov, A. I.; Mebel, A. M. Formation Mechanism of Polycyclic Aromatic Hydrocarbons beyond the Second Aromatic Ring. J. Phys. Chem. A 2013, 117, 4794-4816. (63) Parker, D. S. N.; Kaiser, R. I.; Bandyopadhyay, B.; Kostko, O.; Troy, T. P.; Ahmed, M. Unexpected Chemistry from the Reaction of Naphthyl and Acetylene at Combustion-Like Temperatures. Angew. Chem. Int. Ed. 2015, 54, 5421-5424. (64) Li, Y.; Zhang, L.; Tian, Z.; Yuan, T.; Wang, J.; Yang, B.; Qi, F. Experimental Study of a Fuel-Rich Premixed Toluene Flame at Low Pressure. Energy & Fuels 2009, 23, 1473-1485. (65) Kislov, V. V.; Mebel, A. M. Ab Initio G3-type/Statistical Theory Study of the Formation of Indene in Combustion Flames. I. Pathways Involving Benzene and Phenyl Radical. J. Phys. Chem. A 2007, 111, 3922-3931. (66) Matsugi, A.; Miyoshi, A. Reactions of o-Benzyne with Propargyl and Benzyl Radicals: Potential Sources of Polycyclic Aromatic Hydrocarbons in Combustion. Phys. Chem. Chem. Phys. 2012, 14, 9722-9728. (67) Nyquist, R. A.; Potts, W. J. Infrared absorptions characteristic of the terminal acetylenic group (-CC-H). Spectrochim. Acta 1960, 16, 419-427. (68) Evans, J. C.; Nyquist, R. A. The Vibrational Spectra and Vibrational Assignments of the Propargyl Halides. Spectrochim. Acta 1963, 19, 1153-1163. (69) Biczysko, M.; Panek, P.; Scalmani, G.; Bloino, J.; Barone, V. Harmonic and Anharmonic Vibrational Frequency Calculations with the Double-Hybrid B2PLYP Method: Analytic Second Derivatives and Benchmark Studies. J. Chem. Theory Comput. 2010, 6, 2115-2125. (70) Shukla, B.; Koshi, M. Importance of Fundamental sp, sp2, and sp3 Hydrocarbon Radicals in the Growth of Polycyclic Aromatic Hydrocarbons. Anal. Chem. 2012, 84, 5007-5016. 31 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(71) Friedrichs, G.; Goos, E.; Gripp, J.; Nicken, H.; Schönborn, J.-B.; Vogel, H.; Temps, F. The Products of the Reactions of o-Benzyne with Ethene, Propene, and Acetylene: A Combined Mass Spectrometric and Quantum Chemical Study. Z. Phys. Chem. 2009, 223, 387. (72) Lifshitz, A.; Tamburu, C.; Dubnikova, F. Reactions of 1-Naphthyl Radicals with Acetylene. Single-Pulse Shock Tube Experiments and Quantum Chemical Calculations. Differences and Similarities in the Reaction with Ethylene. J. Phys. Chem. A 2009, 113, 10446-10451. (73) Porter, G.; Steinfeld, J. I. Rate of Dimerisation of Gaseous Benzyne. J. Chem. Soc. A 1968, 877-878. (74) Osborn, D. L.; Zou, P.; Johnsen, H.; Hayden, C. C.; Taatjes, C. A.; Knyazev, V. D.; North, S. W.; Peterka, D. S.; Ahmed, M.; Leone, S. R. The Multiplexed Chemical Kinetic Photoionization Mass Spectrometer: A New Approach to Isomer-Resolved Chemical Kinetics. Rev. Sci. Instrum. 2008, 79. (75) Taatjes, C. A.; Hansen, N.; Osborn, D. L.; Kohse-Höinghaus, K.; Cool, T. A.; Westmoreland, P. R. "Imaging" Combustion Chemistry via Multiplexed SynchrotronPhotoionization Mass Spectrometry. Phys. Chem. Chem. Phys. 2008, 10, 20-34. (76) Hemberger, P.; Trevitt, A. J.; Ross, E.; da Silva, G. Direct Observation of paraXylylene as the Decomposition Product of the meta-Xylyl Radical Using VUV Synchrotron Radiation. J. Phys. Chem. Lett. 2013, 4, 2546-2550. (77) Holzmeier, F.; Wagner, I.; Fischer, I.; Bodi, A.; Hemberger, P. Pyrolysis of 3Methoxypyridine. Detection and Characterization of the Pyrrolyl Radical by Threshold Photoelectron Spectroscopy. J Phys. Chem. A 2016, 120, 4702-4710. (78) Oßwald, P.; Hemberger, P.; Bierkandt, T.; Akyildiz, E.; Köhler, M.; Bodi, A.; Gerber, T.; Kasper, T. In situ Flame Chemistry Tracing by Imaging Photoelectron Photoion Coincidence Spectroscopy. Rev. Sci. Instrum. 2014, 85, 025101. (79) Richter, H.; Benish, T. G.; Mazyar, O. A.; Green, W. H.; Howard, J. B. Formation of Polycyclic Aromatic Hydrocarbons and their Radicals in a Nearly Sooting Premixed Benzene Flame. Proc. Combust. Inst. 2000, 28, 2609-2618. (80) Raj, A.; Al Rashidi, M. J.; Chung, S. H.; Sarathy, S. M. PAH Growth Initiated by Propargyl Addition: Mechanism Development and Computational Kinetics. J. Phys. Chem. A 2014, 118, 2865-2885. (81) Chen, P. In Unimolecular and Bimolecular Reaction Dynamics; Ng, C. Y., Baer, T., Powis, I., Eds.; Wiley: New York, 1994, p 371-425. (82) Klippenstein, S. J.; Miller, J. A.; Jasper, A. W. Kinetics of Propargyl Radical Dissociation. J. Phys. Chem. A 2015, 119, 7780-7791. (83) Steinbauer, M.; Lang, M.; Fischer, I.; de Miranda, B. K. C.; Romanzin, C.; Alcaraz, C. The Photoionisation of Propargylene and Diazopropyne. Phys. Chem. Chem. Phys. 2011, 13, 17956-17959. (84) Moskaleva, L. V.; Madden, L. K.; Lin, M. C. Unimolecular Isomerization/Decomposition of ortho-Benzyne: Ab Initio MO/Statistical Theory Study. Phys. Chem. Chem. Phys. 1999, 1, 3967-3972. (85) Ghigo, G.; Maranzana, A.; Tonachini, G. o-Benzyne Fragmentation and Isomerization Pathways: a CASPT2 Study. Phys. Chem. Chem. Phys. 2014, 16, 23944-23951.

TOC Figure:


Page 32 of 45

Page 33 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60




IR

UV abs.

m/z = 178

abs.

m/z = 128 m/z = 126

ΔT TOF-MS

abs.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Page 34 of 45

ACS Paragon Plus Environment

Page 35 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1 282x286mm (300 x 300 DPI)



2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

7 6

2 8 0

3 0 0

1 1 8 n m S P I

3 9 5 0 7 8 7 4

1 5 2 1 5 6 1 5 8

1 1 5

5 2

io n s ig n a l [a .u .]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Page 36 of 45

3 8

2 6 3 n m (R E )M P I

1 4 9 1 5 4 1 7 8 1 2 8 1 0 2

2 0

4 0

6 0

8 0

1 0 0

2 2 6 2 2 8

1 7 6

1 2 6

1 2 0

2 0 2 2 0 0

1 4 0

1 6 0

1 8 0

m /z [a m u ]


2 0 0

2 2 0

2 5 2 2 5 0

2 4 0

2 6 0

2 8 0

3 0 0

Page 37 of 45

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

2 6 3 n m

s ig n a l

IR /U V m /z = 7 8 b e n z e n e F T -IR

IR

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45


6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

w a v e n u m b e r /c m


-1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0


6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 2 8 IR /U V 2 7 5 .3 n m

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Page 38 of 45

n a p h th a le n e c o m p u ta tio n

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0



1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

Page 39 of 45

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 5 4 IR /U V 2 7 0 n m

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45


b ip h e n y l c o m p u ta tio n

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0



1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0


6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 7 8 IR /U V 2 7 5 .3 n m

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Page 40 of 45

p h e n a n th re n e c o m p u ta tio n

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0



1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

Page 41 of 45

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 2 2 8 IR /U V 2 6 3 n m

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45


b e n z o [a ]a n th ra c e n e c o m p u ta tio n

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0



1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0


6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 1 6 IR /U V a ll W L

in d e n e F T -IR

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

Page 42 of 45

6 x

1 -p h e n y lp r o p y n e F T -IR

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

w a v e n u m b e r /c m ACS Paragon Plus Environment

1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

Page 43 of 45

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 0 2 IR /U V a ll W L

m /z = 1 2 6 IR /U V 2 6 3 n m

m /z = 1 5 0 IR /U V 2 7 0 n m

m /z = 1 5 2 IR /U V

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2 6 3 + 2 7 5 .3 n m

m /z = 1 7 6 IR /U V a ll W L

m /z = 2 0 2 IR /U V 2 6 3 + 2 7 5 .3 n m

m /z = 2 2 6 IR /U V 2 6 3 + 2 7 5 .3 n m

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0



1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0


6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 2 6 IR /U V 2 6 3 n m

1 ,4 -d ie th y n y lb e n z e n e F T -IR

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

Page 44 of 45

1 ,4 -d ie th y n y lb e n z e n e c o m p u ta tio n

v ib r a tio n a l b a n d s : fu n d a m e n ta l c o m b in a tio n o v e rto n e

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0


1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

Page 45 of 45

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

m /z = 1 5 2 IR /U V 2 6 3 + 2 7 5 .3 n m

2 -e th y n y ln a p h th a le n e F T -IR

IR s ig n a l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58


2 -e th y n y ln a p h th a le n e c o m p u ta tio n

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0


1 3 0 0 -1

1 4 0 0

1 5 0 0

1 6 0 0

1 7 0 0

Products of the Propargyl Self-Reaction at High Temperatures

Recommend Documents