Formation of HCO+ and HCS+ Ions in the Photodissociation of

Subscriber access provided by UNIV OF SOUTHERN INDIANA

A: Spectroscopy, Molecular Structure, and Quantum Chemistry

Formation of HCO+ and HCS+ Ions in the Photodissociation of CH3OC(S)SCH3 under VUV Synchrotron Radiation Lucas Sebastián Rodríguez Pirani, Antonela Cánneva, Mariana Geronés, Carlos Omar Della Védova, Rosana Mariel Romano, Reinaldo Luiz Cavasso Filho, and Mauricio Federico Erben J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.9b03670 • Publication Date (Web): 11 Jul 2019 Downloaded from pubs.acs.org on July 22, 2019

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 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 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.

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 34 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

Formation of HCO+ and HCS+ Ions in the Photodissociation of CH3OC(S)SCH3 under VUV Synchrotron Radiation Lucas S. Rodríguez Pirani,1 Antonela Canneva,1,† Mariana Gerones,1 Carlos O. Della Védova,1,* Rosana M. Romano,1 Reinaldo Cavasso-Filho,2 Mauricio F. Erben1* 1- CEQUINOR (UNLP – CONICET, CCT La Plata, associated with CIC PBA). Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata. Boulevard 120 e/ 60 y 64 Nº1465, La Plata (CP 1900), República Argentina. 2- Universidade Federal do ABC, Rua Catequese, 242, CEP: 09090-400, Santo André, São Paulo, Brazil.

† Current adress: CONICET, YPF TECNOLOGÍA S. A. (Y-TEC), Av. del Petróleo s/n, Entre 129 y 143, Berisso, Buenos Aires 1925, Argentina.

*To whom correspondence should be addressed. Tel: +54-221-4454393. E-mail: [email protected] (MFE), [email protected] (CODV).

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry 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 2 of 34

Abstract Synchrotron-based Total Ion Yield (TIY) and PhotoElectron-PhotoIon-Coincidence (PEPICO) spectra have been applied to investigate the electronic structure and the dissociative ionization of gaseous O,S-dimethyl xanthate, CH3OC(S)SCH3, in the shallow-core S 2p region. The spectral assignment and the electronic structure are interpreted in terms of the most stable synperiplanar conformer in the CS symmetry point group. The use of tunable synchrotron radiation allows for a selective excitation of sulfur atoms at different photon energy values, including resonance transitions and ionization around the S 2p level. The fragmentation patterns show that the title molecule is well suited as a laboratory precursor of ionic species found in the interstellar medium, especially formyl and thioformyl cations, HCO+ and HCS+, respectively.


2

Page 3 of 34 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


1- Introduction Xanthates (from the Greek “golden”) are the esters of xanthic acid, with general formula ROC(S)SR'. These are important organosulfur compounds used in the production of cellophane and as flotation agents for extraction of metals from many ores. As an example, sodium ethyl xanthate is added as a collector in the selective flotation of PbS (galena) to separate it from ZnS.1-3 The absorption of xanthate in natural pyrite was studied with X-ray Photoelectron Spectroscopy, showing that xanthate species predominate at 6 ≤ pH ≤ 10, whereas dixanthogen species are formed in the surface of the ore in oxidizing conditions.4-5 The capacity of xanthates as ligand in coordination chemistry is also widely recognized.6-9 The photoevolution of xanthate compounds is characterized by a homolytic scission of the C–S bond yielding phenacyl and xanthic acid radicals, as determined by flash photolysis studies.10 One of the simplest member of the xanthate family is CH3OC(S)SCH3, namely dimethyl xanthate or O,S-dimethyl dithiocarbonate. This species was first synthesized by Douglass and Evers in 196411 and early studies on the chemistry and spectroscopy of organic xanthates were developed by the group of Gattow.12 More recently, the reaction of CH3OC(S)SCH3 with the super acidic system XF/MF5 (X= H, D; M = As, Sb) yields the protonated mercapto methoxy methylthio carbenium hexafluorometallates, as determined by spectroscopic and X-ray crystal structure determinations.13 A series of xanthate and xanthogen derivatives are also being the subject of investigation in our group, including synthetic aspects together with the elucidation of structural, conformational and vibrational properties.14 The photoelectron spectrum of CH3OC(S)SCH3 in the valence region (7.5-13 eV energy range) was reported by Guimon et al. in 1974 and interpreted in terms of ionization of non-bonded orbital mostly localized on the sulfur atoms.15 The electron


3


Page 4 of 34

impact mass spectra of CH3OC(S)SCH3 was also early reported, and the preponderance of prominent peaks corresponding to CH3S+, HCS+, CH3O+ and HCO+ ions were interpreted in terms of α-cleavage around the central thiocarbonate group.16 It is well-known that the formation of HCS+ is thermodynamically favored and this ion is one of the most abundant sulfur-containing species in the interstellar medium.17-20 On the other hand, the formyl ion, HCO+, is also fairly abundant in the interstellar medium and was first discovery in 1970 by Buhl and Snyder search for hydrogen cyanide (HCN). Shortly after, Klemperer

22

21

during the

corroborated the

presence of HCO+ which was then validated by theoretical chemical models in which ion–molecule reactions were considered as the main sources forming this cation.23 In this scheme, the production of the stable HCO+ ion is due to the proton transfer reaction between H3+ and CO.24 Protonated molecular hydrogen, H3+, is produced through cosmic ray ionization of molecular hydrogen followed by the reaction of H2+ with H2. The steady-state concentration is low because of its extremely high chemical reactivity, since H3+ is a powerful protonating agent, initiating chains of ion−molecule reactions.2526

The main removal mechanism for H3+ is the reaction with the abundant CO molecule.

In the laboratory, the H3+ ion was detected in the microsecond time scale as a weak signal in the time-of-flight mass spectra of CH3C(O)SCH3 irradiated with VUV photons.27 The irradiation of interstellar organic molecules bearing a methyl group, such as acetic acid,28 methanol,29 and methyl formate30 in soft X-ray region , revealed also the formation of formyl cation as an stable photodissociation product.31 Following our general project aimed at elucidating the shallow- and inner–shell core electronic properties and photoionization dynamics of sulfur-containing derivatives,32-33 we became interested in the simplest xanthate compound, ROC(S)SR', with R= R´= CH3. The S 2p core XPS and KLL Auger spectra of CH3OC(S)SCH3 were


4

Page 5 of 34 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


early reported by Suoninen et al.34 showing that the ionization energies of the =S and – S– atoms within the xanthate group differ from each other by 1.5 eV, this difference was assigned to the initial-state charge distribution rather than to final-state relaxation. Prompted by these antecedents, we report here a study of the photon impact excitation and dissociation dynamics of gaseous CH3OC(S)SCH3 excited at the S 2p level by using synchrotron radiation for obtaining the Total Ion Yield (TIY) and PhotoelectronPhotoion-Coincidence (PEPICO) time-of-flight mass spectra.

2- Experimental and Theoretical Methods Synchrotron radiation was used at the Laboratório Nacional de Luz Síncrotron (LNLS), Campinas, São Paulo, Brazil.35 Linearly polarized light monochromatized by a toroidal grating monochromator (available at the TGM beam line in the range 11.2–300 eV),36 intersects the effusive gaseous sample inside a high-vacuum chamber, with base pressure in the range 10–8 mbar. Thus, gaseous CH3OC(S)SCH3 in equilibrium with the liquid sample arrives to the measurement chamber. The gas-jet needle was mounted on a xyz manipulator and the optimal position determined by scanning and obstructing the light by the needle while monitoring the light intensity in perpendicular positions of the beam with a light-sensitive diode. The FWHM of the light beam was determined to be 1 mm.37 During the experiments the pressure was maintained below 510–6 mbar. The resolution power is better than 400 in the TGM beam-line at the LNLS and the energy calibration was established by means of the S 2p → 6a1g and S 2p → 2t2g absorption resonances in SF6.38 The ions produced by the interaction of the gaseous sample with the light beam were detected using a time-of-flight (TOF) mass spectrometer of the Wiley–McLaren type for PEPICO measurements.39-40 This instrument was constructed at the Institute of Physics, Brasilia University, Brasilia, Brazil.41 The spectrometer is


5


Page 6 of 34

cylindrically symmetric and the axis of the TOF spectrometer was perpendicular to the photon beam and parallel to the plane of the storage ring. Electrons were accelerated to a multi channel plate (MCP) and recorded without energy analysis. This event starts the flight time determination process of the corresponding ion, which is consequently accelerated to another MCP. The characteristics and performance of this electron-ion coincidence TOF spectrometer has been reported elsewhere.37 The average kinetic energy release (KER) values of the fragments were calculated from the coincidence spectra by assuming an isotropic distribution of the fragments, and that they are perfectly space focused and that the electric field applied in the extraction region is uniform.42 Under these conditions, the energy release in the fragmentation process can be determined from the peak width (FWHM).43 Deviations from ideal conditions always increase the peak width, thus the values calculated are upper bounds. Santos et al.44 have measured the argon mass spectrum under very similar experimental conditions and a peak width value of 0.05 eV was achieved for the Ar+ ion. Because the broadening in argon can only be the result of thermal energy and instrumental broadening, this value represents a good estimation for the instrumental resolution. OVGF calculations using the cc-pVTZ basis set and B3LYP/aug-cc-pVTZ optimized geometry of CH3OC(S)SCH3 have been performed using the Gaussian 03 program package.45 O,S-Dimethyl Xanthate, CH3OC(S)SCH3 was prepared by treating a methanol solution of potassium methyl xanthate with methyl iodide until 40°(2).11 After standing overnight the reaction mixture was diluted with water and the crude xanthate ester was separated, dried and distilled. CH3OH + CS2 + KOH  CH3OC(S)SK + H2O


(1)

6

Page 7 of 34 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


CH3OC(S)SK + CH3I  CH3OC(S)SCH3 + KI

(2)

The liquid product was purified by fractional distillation. The final purity of the compound was carefully checked by FTIR (vapor), Raman (liquid) and gas chromatography–mass spectrometry.

3- Results and Discussion The molecular structure and conformational properties determine the electronic configuration and define the ionization energies of complex molecules.46 As far as we know, the molecular structure of CH3OC(S)SCH3 has not been studied up to now. In a first approximation, the conformational landscape for the title molecule depends on the orientation of the O-CH3 and S-CH3 groups relative to the C=S double bond, which can be synperiplanar (sp) or antiperiplanar (ap). The potential functions for internal rotation around the C-O and C-S bonds were calculated [B3LYP/6-31+G(d)] by geometry optimizations at fixed torsional angles (see Figure 1). As expected, both curves possess minima for sp Φ (CO-C(S)) = Φ (CS-C(S)) = 0° and ap Φ (CO-C(S)) = Φ (CS-C(S)) = 180° orientations. Thus, in principle at least four conformations are feasible for this compound (see Figure 2).


7


10

Relative Energy (kcal/mol)

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 8 of 34

8

6

4

2

0 0

30

60

90

120

150

180

(C-X-C=S)

Figure 1. Potential energy curve for CH3OC(S)SCH3 as a function of the dihedral angle (C-X-C=S) with X= O (black) and S (red), calculated with the B3LYP/6-31+G(d) approximation. For each calculation the non-variable torsion angle was set to 0°.

Further quantum chemical calculations have been performed by increasing the basis set quality up to the Dunning's correlation consistent triple-zeta basis sets augmented with diffuse functions (aug-cc-pVTZ).47 The relative energies (corrected by zero point energy) and Gibbs free energies are shown in Table 1. According with these calculations, the most stable conformation of CH3OC(S)SCH3 in the ground electronic state is the sp-sp conformer, which belongs to the Cs point group of symmetry. The spap form is the second more stable conformer, computed at 1.28 kcal/mol higher in energy (∆E°). A third form, corresponding to an ap-sp orientation, is calculated at 4.93 kcal/mol (∆E°) above the most stable sp-sp form, whereas the ap-ap conformation resulted to be not a minimum in the potential energy curve.


8

Page 9 of 34 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


∆G° = 0.00 kcal/mol (sp-sp)

∆G° = 1.20 kcal/mol (sp-ap)

∆G° = 4.93 kcal/mol (ap-sp)

Not a minimum (ap-ap)

Figure 2. Conformers of CH3OC(S)SCH3 and their relative energies calculated with the B3LYP/aug-cc-pVTZ level of approximation.

Table 1. Calculated Relative energy for Stable Conformers

of

CH3OC(S)SCH3

in

the

Ground

Electronic State (kcal/mol). CH3OC(S)SCH3 (kcal/mol) sp-sp sp-ap ap-sp B3LYP/6-311+G(d) ∆E° ∆G° B3LYP/6-311++G(d,p) ∆E° ∆G° B3LYP/aug-cc-pVTZ ∆E° ∆G°

0.00a 0.00d

1.10 1.00

5.43 5.40

0.00b 0.00e

1.26 1.18

4.91 4.91

0.00c 0.00f

1.28 1.20

4.93 4.93


9


Page 10 of 34

aE°=-989.539010

Hartree, bE°= -989.575061 Hartree, cE°= 989.584727, dE°= -989.571661, eG°= -989.607751 Hartreee, fG°= -989.617456 Hartree

3.1- Total Ion Yield Spectra (TIY) TIY spectra of CH3OC(S)SCH3 have been obtained near the S 2p edge by recording the count rates of ions while the photon energy is varied in the 160.0-180.0 eV range, as shown in Figure 3. The spectrum is dominated by a group of well-defined signals between 164.0 and 169.0 eV, below the S 2p ionization threshold. The well resolved structures observed in the TIY spectrum can be interpreted as originated by electronic transitions involving the spin-orbit split of the S 2p excited species (2p1/2 and 2p3/2 levels) to the lower unoccupied antibonding orbitals. The characters of the highest occupied and unoccupied molecular orbital of the most stable sp-sp conformer have been calculated using B3LYP/aug-cc-pVTZ level of approximation (Figure 4). All canonical molecular orbitals of type a´ are σ orbitals lying in the symmetry plane, whereas those of type a´´ are π orbitals. The HOMO and HOMO-1 can be visualized as orbital having a´ and a´´ symmetry, respectively, nominally localized on different sulfur atoms in the central xanthate group, and occupied by lone-pair electrons [n´(S) and n´´(S) in Figure 4]. On the other hand, the LUMO corresponds to a π*C=S (a´´) orbital with antibonding character localized in the C=S thiocarbonyl group. The next vacant orbitals correspond to the antibonding σ*C-S (CH3-S) (a´), σ*S-C (S-C(S)) (a´), and σ*O-C (CH3-O) (a´).


10

Page 11 of 34

1.0

=S 168.2 eV

Ion Signal (u.a.)

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


-S169.7 eV

0.8

0.6 165.8 eV 167.4 eV

0.4 164.4 eV

0.2 160

164

168

172

176

180

Photon Energy (eV)

Figure 3. Total ion yield spectrum of CH3OC(S)SCH3 near to the S 2p edge. The S 2p ionization energies reported by Suoninen et.al. are indicated by the vertical lines.34

HOMO n´ (S)

HOMO -1 n´´ (S)

HOMO -2 π (C=S)

HOMO -3 n´´ (O)

LUMO π*(C=S)

LUMO +1 σ*(C-S)

LUMO +2 σ*(S-C(S))

LUMO +3 σ*(O-C)

Figure 4. Characters of the frontier orbitals of CH3OC(S)SCH3 calculated at the B3LYP/6-311+G(d,p) levels of approximation.

The first signal in the TIY at 164.4 eV is assigned to the S 2p→ π*(C=S) transition involving the core electrons from the thiocarbonyl C=S sulfur with a´´ symmetry. The


11


Page 12 of 34

most intense resonance observed at 165.8 eV, with a shoulder at slightly lower energy (165.1 eV) are assigned to the dipole allowed S 2p→ σ*(C-S) and S 2p→ σ*(S-C(S)) transitions, respectively, involving the C-S antibonding orbitals with a´ symmetry strong sulfur-p character. This band is observed in the TIY spectrum as a rather broad signal probably denoting the contribution from both C=S and –S– sulfur atoms as well as the unresolved splitting of the 2p1/2 and 2p3/2 levels. The last transition defined as a low intense band at 164.7 eV, just below the ionization threshold, is attributed to the S 2p→ σ*(O-C) transition. The ionization energies for the sulfur 2p level of the C=S and –S– groups are 168.2 and 169.7 eV respectively, as reported by Suoninen et.al. from XPS and KLL Auger spectra.34 In perfect agreement with these features, the TIY spectrum shows a pronounced signal enhancement at 168.1 eV photon energy, which can be associated to the ionization continuum. The splitting found for the ionization energy is attributed to the initial-state charge distribution (Scheme 1) between singly and double bonded sulfur. The resonance electronic contribution lowers the ionization energy of =S and increases that of the –S-. This effect is also reflected in the outermost valence orbital, in which the energy difference between HOMO and HOMO-2, i.e. the sulfur lone pair and the π(C=S) (Figure 3), is 1.4 eV, as calculated using OVGF/6-311++G(d,p) level of approximation.

S

S

C

C

S

S

Scheme 1. Mesomeric effect in the xanthate group involving sulfur atoms.


12

Page 13 of 34 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


3.2- Ionic dissociation Several PEPICO spectra have been recorded by setting the photon energy at the resonant values obtained in the TIY spectrum in the S 2p region. In order to identify the role of resonant processes in the fragmentation, spectra were also measured at photon energy values below (typically 10 eV) and above (typically 50 eV) the ionization edge. The PEPICO spectra taken at representative photon energies near to the S 2p edge of CH3OC(S)SCH3 are shown in Figure 5. In Table 2 the corresponding branching ratios for the main fragment ions are also shown. The PEPICO spectrum of the sample irradiated with photons of 155 eV of energy, corresponding to excitation energies in the valence continuum, is good reference to compare the effect of excite/ionize sulfur 2p electrons. At this energy, the single-charged parent ion is observed with the relative abundance of 4.1 %. A strong signal at m/z = 15 amu/q, corresponding to the methyl ion CH3+, is the most abundant ion appearing in the spectrum, amounting up to 17.2 %. This ion can be originated by the α-bond scission of both H3C-O or H3C-S single bond in the single ionized CH3OC(S)SCH3·+. The following resonant structures present in the parent ion lead to formation of CH3+ ion (Scheme 2).16

S CH3

C

H3C O

CH3+ + CH3SC(S)O

S

S CH3

C

H3C O

S S CH3

C

H3C O

CH3+ + CH3OC(S)S

S


13


Scheme 2. Formation of CH3+ ion following the H3C-O or S-CH3 ruptures of simple ionized CH3OC(S)SCH3·+.

3.0 CH3+ 2.5

HxCS

+

H

+

(x=0-3)

E= 173.8 eV

2.0 Counts (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 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 34

E= 167.5 eV

1.5 S

+

CH3S

+

+

CH3OC(S)

E= 165.9 eV

1.0 +

HCO

OCS

+

SS

+

C(S)S

+

E= 164.4 eV

0.5 C(S)SCH3+

CH3OC(S)SCH3+ E= 155.0 eV

0.0 0

20

40

60 80 Mass/Charge (a.m.u./q)

100

120

140

Figure 5. PEPICO spectra of CH3OC(S)SCH3 irradiated with photons around the S 2p edge.

Other peaks with appreciable intensities observed in the spectrum correspond to the HCS+, H3CS+ and CH3OC(S)+ ions, with relative abundances of 12.2, 8.8 and 6.4 % respectively. The appearance of the HxCS+ series can be explained by the rupture of C– S single bond from the parent ion, following by the loss of hydrogen atoms. The HCS+ ion has been frequently observed in the ionic fragmentation of other sulfur compounds having a methyl group attached to the sulfur atom, as previously founded for ClC(O)SCH3,48 CH3SCN,49 FC(O)SCH3 and CH3C(O)SCH3.27 These observations suggest that the rupture of the C–S bond is one of the most important events after valence continuum excitations in CH3OC(S)SCH3·+ (Scheme 3).


14

Page 15 of 34 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


S H3C

CH3

C O

SCH3+ + CH3OCS

S

SCH3+

HCS+ + H2

Scheme 3. Formation of HCS+ ion following the C-S rupture of simple ionized CH3OC(S)SCH3·+.

Previous studies performed by Holm and Schroll on the mass spectra of alkyl dithiocarbonates,16 showed the higher stability of the CH3-S radical as compared with the CH3-O radical. In line with this finding, photofragmentation processes involving the rupture of O-C(S) single bond from CH3OC(S)SCH3·+ seem to be of minor importance. Only the weak peak at m/z = 91, assigned to the loss of a CH3O group from the parent ion, is observed with relative abundance between 1-2 %. Despite of the absence of the CH3O+ ion (M+-91), HxCO+ (x= 0, 1, 2) ions are observed in the spectrum with relative low abundances between 2-4 %. The following simple mechanisms from the single charged parent ion could occur: CH3OC(S)SCH3+ → CH3O+ + C(S)SCH3 CH3O+ → CH2O+ + H CH3O+ → HCO+ + H2 The photofragmentation of CH3OC(S)SCH3 reveals a preferential production of HCO+ ions, while signals corresponding to the ionic fragments CO+ and CH2O+ are observed with lower relative intensity, whereas the CH3O+ ion could not be observed in the spectra. These results are in good agreement with those found in the dissociative photoionization process of the related species CH3OC(O)SCl irradiated with soft X-ray photons, for which small quantities of formyl cation was detected by using photoelectron−photoion coincidence techniques. It should be noted that the intensity of


15


Page 16 of 34

HCO+ was always higher than the other fragments of the series of CHxO+ (x = 0, 2 and 3) ions.27 This behavior is different to that observed by the electron impact ionization of CH3OC(S)SCH3, where the CH3O+ ion was observed with larger relative intensity than the other fragments in the CHxO+ (x = 0-3) series.16 Another striking absence is a process involving the loss of a CH3 group as neutral fragment from the parent ion. The high affinity positive charge of the CH3 moiety when H3C-O or S-CH3 single bond is broken could be the cause of this lack. A very weak peak at m/z = 62 is also observed in the 155.0 eV PEPICO spectrum. The presence of this ion was also detected in the electron impact mass spectrum of CH3OC(S)SCH3 and correspond at the ionized dimethyl sulfide.16 This ion could be formed by an elimination of neutral carbonyl sulfide, according to the following skeletal rearrangement: CH3OC(S)SCH3·+ → (CH3)2S·+ + OCS Then, signals located at m/z = 59, 60 and 61 amu/q also appear in this spectra and they could be originated by the loss of hydrogen atoms from both methyl groups of the dimethyl sulfide ion. In particular, the signal with m/z = 60 could be also due to the formation of the OCS+ ion (See Figure 6).


16

Page 17 of 34

1.0 0.08

+ (C2H4)S+/OCS 0.8

S2+

Counts (a.u.)

counts (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 46


0.6

(CH3)2S+

0.04

0.4 0.00 56

58

60

62

64

66

Mass/Charge (a.u.m./q)

0.2

0.0 0

20

40


100

120

140

Figure 6. PEPICO spectrum of CH3OC(S)SCH3 irradiated at 155 eV. Enlargement of the m/z region corresponding to (C2Hx)S+ (x = 3-6), OCS+ and S2+ ions.


17


Page 18 of 34

Very similar PEPICO spectra are obtained when different photon energies are used and the S 2p transition resonances are analyzed, showing that small site-specific effects occur in the photofragmentation of CH3OC(S)SCH3. However, interesting changes can be noted as compared between the in-resonance with the valence continuum spectra. As already commented, the main contribution to the PEPICO spectra below the S 2p threshold comes from fragmentation of single charged parent ion. However, when the normal Auger processes take place at S 2p ionization energies, double charged parent ion are formed, producing changes in the photodisociation channels. The peak corresponds to the single-charged parent ion clearly diminishes its intensity, reaching values of only 1.5% when the S 2p edge is reached. A strong signal at m/z = 15 amu/q, corresponding to CH3+ ion, dominates the PEPICO spectrum in the S 2p region. The next most abundant ion observed in the spectra corresponds to the HCS+ fragment. In effect, the analysis of the PEPICO spectra of CH3OC(S)SCH3 over the whole range of photon energies reveals a preferential production of HCS+ ions, while signals corresponding to ionic fragments CS+, CH2S+, and CH3S+ appear as less intense peaks. This behavior is opposite to that observed in the mass spectra by electron impact ionization where the CH3S+ ion is the most intense than of the series CHxS+ (x = 0–3) fragments.16 Other prominent ions observed with relative abundances between 4 and 8 % are: H+ (m/z= 1), CH2+ (m/z= 14), HCO+ (m/z= 29), and S+ (m/z= 32). The description of spectra is complemented by the presence of the following less abundant fragments: CHx+(x= 0, 1) with m/z= 12 and 13, O+/S+2 (m/z= 16), CHxO+ (x= 0, 2) with m/z= 28, 30, and SH+ (m/z= 33), CH3OC+ (m/z= 43), CS+ (m/z= 44), OCS+ (m/z= 60), S2+ (m/z= 64), CH3OCS+ (m/z= 75), and CH3SC(S)+ (m/z= 91).


18

Page 19 of 34

Especial attention deserves the group of signals appearing at m/z = 76, 77, 78, and 79 amu/q, associated with the ions CSS+, CHSS+, CH2SS+, and CH3SS+, respectively, formed from the xanthate moiety (see Figure 7). It is important to note that the formation of disulfide bond in CH3SS+ (m/z= 79) ion is a typical signature of processes involving rearrangement reactions from the CH3SC(S)+ fragment. The formation of CHxSS+ (x= 0- 2) ions could be explained by the loss of neutral hydrogen atoms from the CH3SS+ fragment. Probably, the formation of SS+ ion with m/z = 64, could be possible via some of the CHxSS+ ions formed in the first step. A diminution in the m/z= 75 amu/q peak intensity, corresponding to the CH3OC(S)+ ion, is observed as the photon energy increases. This fact can be correlated with the concomitant enhancement in the signal intensity of the ions CH3+ and OCS+ by going toward higher energies. It is plausible that ruptures of C-S bonds are promoted when the S 2p are selectively excited at resonance transitions using 164.4 and 165.9 eV energy photons.

CH3OC(S)+ CSS+

0.3

Counts (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 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CHSS+

0.2

0.1

CH3SS+

0.0 72

74

76

78


80

82


19


Page 20 of 34

Figure 7. Enlargement of the m/z region corresponding to CH3OC(S)+ and CHxSS+ (x= 0-3) ions of the PEPICOs spectra of CH3OC(S)SCH3 at 155 eV (off-resonance, red line) and 164.4 eV (in-resonance, black line).

3.3- Kinetic Energy Release (KER) analysis The kinetic energy release (KER) values have been determined from the full width at half-maximum of the signals observed in the PEPICO spectra.42-43 This energy is associated with the photofragmentation process, in which the internal energy of the parent ion is released as kinetic energy of the fragments. As commented before, contributions from both single and multiple ionization process are expected to be detected in the PEPICO spectra in the studied energy range, because the decay of core shell excited species usually promotes the formation of doubly charged parent ion in several excited states. Since different internal energies are associated with each cationic charge, the analysis of the KER values is very useful for identifying the occurrence of fragmentation process from single or double charged parent ions. The C(S)SCH3+ (m/z= 91) and CH3OC(S)+ (m/z= 75) ions, that correspond to the heaviest fragments detected, are necessarily produced from the singly charged parent ion, since only the lightest fragment is detected in the PEPICO spectra. This hypothesis agrees with relative low KER values determined for these ions in the whole range of photon energies analyzed (see Table 2). The following simple mechanisms explain the experimental observation.

CH3OC(S)SCH3+ → CH3OC(S)+ + SCH3 (KER = 0.05 eV) CH3OC(S)SCH3+ → C(S)SCH3+ + OCH3 (KER = 0.05 eV)


20

Page 21 of 34 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


When the photon energy reaches the S 2p ionization edge, normal Auger decay prevails, the dissociation channels from doubly charged ions are enhanced and broader peaks are anticipated to be observed. In line with these expectations, lighter species such as CHx+, S+, CHxO+, CHxS+ or SCH3+ dominates the PEPICO spectra near the S 2p edge, generated through photofragmentation processes that involve singly and/or doubly charges species. These photodissociation events from multiple charge ions lead to higher KER values, as can be observed in Table 2. For example, the following mechanisms could be associated to the formation of HCX+ ion (X= O or S) from doubly charged parent ion:27, 50 CH3OC(S)SCH32+ → CH3YC(S)+ + XCH3+

(Y= O , X= S or Y= S, X=O)

XCH3+ → HCX+ + H2

(KER= 0.24-0.81 eV) (X= S) (KER= 0.48-1.18 eV) (X= O)

Figure 8, depicts the PEPICO spectra for m/z corresponding to the HxCX+ (x = 0-3, X= O and S) ions at 165.9 and 173.8 eV of energy. The increment in the KER is apparent from the observed broadening of these peaks. For example, the KER values for the HCO+ ion (panel a of Figure 8) increases from 0.48 eV at 165.9 eV up to 1.18 eV when the sample is irradiated with photons of 173.8 eV, while for HCS+ ion (panel b of Figure 8) increases from 0.21 up to 0.81 eV in the same range of photon energies.


21


+ HCS

b)

a) 0.4

0.2 + HCO

0.1

+ CO

+ H3CS

0.3

Counts (a.u.)

Counts (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 46

Page 22 of 34

+ H2CO + H3CO

173.8 eV

+ H2CS

0.2 + CS

0.1 173.8 eV

165.9 eV

165.9 eV

0.0

0.0 26

28

30

32

34

40

42

44

46

48

50



Figure 8. Enlargements of the m/z regions corresponding to the HxCS+ ions (panel a) and the HxCO+ ions (panel b), of the PEPICO spectra of CH3OC(S)SCH3 irradiated around the S 2p edge, 165.9 (black) and 173.8 eV (red).


22

Page 23 of 34 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


Table 2. Branching ratios (%) for fragment ions extracted from PEPICO spectra taken at photon energies around the S 2p edge for CH3OC(S)SCH3 molecule. Kinetic energy release values (in eV) determined from the spectra are given in italics. m/z 1 2 12 13 14 15 16 28 29 30 31 32 33 43 44 45 46 47 60 61 62 64 75 76 77 79

Ion H+ H2+ C+ CH+ CH2+ CH3+ O+/S+2 CO+ HCO+ CH2O+ CH3O+ S+ SH+ CH3OC+ CS+ HCS+ H2CS+ CH3S+ OCS+ C2H5S+ C2H6S+ SS+ CH3OCS+ C(S)S+ C(S)SH CH3SS+

155.0 4.7 1.6 4.8 17.2 1.2 2.4 3.8 1.7 1.2 4.7 1.3 1.1 2.5 12.2 4.3 8.8 1.9 1.7 1.1 1.6 6.4 2.2 1.1 1.2

164.4 4.9/--1.0 1.8/0.4 2.5/0.6 5.8/0.8 17.9/0.04 1.1 1.6/0.2 4.2/0.6 1.6/--0.5 6.3/0.3 1.5/0.1 1.0 2.9/0.5 13.2/0.2 4.6/0.2 6.2/0.1 2.4/0.1 1.0 1.7/0.09 3.5/0.05 2.2/0.1 0.7/0.05 0.9/0.2

165.9 4.4/--1.0 2.1/0.3 2.6/0.7 5.7/0.6 18.6/--1.4 1.6/0.03 4.0/0.5 1.7/0.07 0.6 6.3/0.3 1.5/--1.6 2.7/0.4 10.7/0.2 3.8/0.2 6.3/0.1 2.8/0.1 0.7 2.3/0.1 3.5/0.05 2.3/0.1 1.2/0.07 1.2/---

Photon energy (eV) 167.5 173.8 4.7/--4.3/--0.9 1.0 2.0/0.5 1.9/0.8 2.6/0.6 2.6/1.2 6.1/0.8 5.6/1.3 18.5/0.05 20.2/0.7 1.1 1.6 1.7/0.3 1.6/0.4 4.3/0.6 4.6/1.2 1.7/ 2.2/0.8 0.7 6.6/0.3 6.0/0.6 1.5/0.2 1.7/0.5 1.1 0.9 3.1/0.6 2.7/0.6 13.6/0.2 12.1/0.8 4.7/0.2 2.7/0.5 6.4/0.2 7.9/0.8 2.3/0.2 2.5/0.5 0.5 1.7/0.1 1.4/0.08 3.6/0.05 3.4/1.3 2.1/0.1 2.2/--0.7/0.03 0.9/--1.0/0.1 1.7/0.2


23

The Journal of Physical Chemistry 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

91 122

C(S)SCH3+ CH3OC(S)SCH3+

1.6 4.1

1.0/0.05 1.5/0.02

1.0/0.06 1.6/0.02

0.9/0.04 1.5/0.02


Page 24 of 34

1.1/--0.8/0.02

24

Page 25 of 34 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


4- Conclusions Electronic properties of the simplest xanthate organic species CH3OC(S)SCH3 in the shallow-core S 2p region were analyzed using multicoincidence time-of-flight mass spectrometry, in combination with synchrotron radiation as monochromatic photon source. The Total Ion Yield spectrum in the S 2p level was recorded and interpreted as resonant transitions due to dipole-allowed transitions from S 2p electrons to antibonding molecular orbitals for the most stable s-sp conformer. Three well-defined signals centered at 164.8, 165.8 and 167.4 eV are assigned to S 2p→ π*(C=S) (a´´), S 2p→ σ*(C-S) (a´) and S 2p→ σ*(O-C) (a´), respectively. The ionic fragmentations associated with each electronic transition have been also analyzed and the PEPICO spectra allow identifying the rupture of the C–S bond as one of the most important events observed throughout the range of energy studied, accounting for ca. 53% of the ions observed in the spectra. Site-specific fragmentations caused by the S 2p level photoionization seem to be absent when the sulfur atoms in both –S– or the C=S groups are individually excited. In agreement with previous VUV photofragmentation studies of organosulfur species possessing the thiomethyl group,27,

48

the fragmentation of CH3OC(S)SCH3

gives origin to the stable interstellar ion HCS+. In addition, the interstellar ion HCO+ has been also observed in this work. The formation of the formyl cation from the title molecule can be originated from the presence of the methyl group attached to the oxygen atom in the xanthate central group. The preferential production of HCO+ and HCS+ ions was observed over the whole series of CHxO+ (x = 0, 2, 3) and CHxS+ (x= 0, 2, 3) fragments. The analysis of the KER distribution suggests that HCO+ and HCS+ ions are formed from both, single and double charged CH3OC(S)SCH3.


25


Page 26 of 34

Acknowledgments This work was supported by the Brazilian Synchrotron Light Source (LNLS) under proposal D05A-TGM-1149. We want to thank the TGM beamline staffs for their assistance during the experiments. We are indebted to the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Agencia Nacional de Promoción Científica y Técnologica (ANPCyT, PICT 2130) and the Facultad de Ciencias Exactas, Universidad Nacional de La Plata, for financial support.

5- References 1.

Giesekke, E. W., A Review of Spectroscopic Techniques Applied to the Study

of Interactions between Minerals and Reagents in Flotation Systems. Int. J. Miner. Process. 1983, 11, 19-56. 2.

Vučinić, D. R.; Lazić, P. M.; Rosić, A. A., Ethyl Xanthate Adsorption and

Adsorption Kinetics on Lead-Modified Galena and Sphalerite under Flotation Conditions. Colloids Surf. A 2006, 279, 96-104. 3.

Grano, S. R.; Prestidge, C. A.; Ralston, J., Solution Interaction of Ethyl Xanthate

and Sulphite and its Effect on Galena Flotation and Xanthate Adsorption. Int. J. Miner. Process. 1997, 52, 161-186. 4.

Szargan, R.; Karthe, S.; Suoninen, E., XPS Studies of Xanthate Adsorption on

Pyrite. Appl. Surf. Sc 1992, 55, 227-232. 5.

Szépvölgyi, J.; Tüdös, A.; Bertóti, I., X-ray Photoelectron Spectroscopy Studies

on Solid Xanthates. J. Electron Spectrosc. Rel. Phenom. 1990, 50, 239-250. 6.

Bailey, J. H. E.; Drake, J. E.; Khasrou, L. N.; Yang, J., Synthesis and

Spectroscopic Characterization of O-Alkyl Dithiocarbonate (Xanthate) Derivatives of


26

Page 27 of 34 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


Dimethyl- and Diphenyltellurium(IV). Crystal Structures of Me2Te[S2COEt]2 and Ph2Te[S2COEt]2. Inorg. Chem. 1995, 34 (1), 124-133. 7.

Davy, J. A.; Mason, J. W.; Moreau, B. t.; Wulff, J. E., Xanthates as Synthetic

Equivalents of Oxyacyl Radicals: Access to Lactones under Tin-Free Conditions. J. Org. Chem. 2012, 77 (14), 6332-6339. 8.

Zard, S. Z., On the Trail of Xanthates: Some New Chemistry from an Old

Functional Group. Angew. Chem. Int. Ed. Engl. 1997, 36 (7), 672-685. 9.

Juncal, L. C.; Avila, J.; Asensio, M. C.; Della Védova, C. O.; Romano, R. M.,

Electronic Structure Determination Using an Assembly of Conventional and Synchrotron Techniques: The Case of a Xanthate Complex. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2017, 180, 183-192. 10.

Tazhe Veetil, A.; Šolomek, T.; Ngoy, B. P.; Pavlíková, N.; Heger, D.; Klán, P.,

Photochemistry of S-Phenacyl Xanthates. J. Org. Chem. 2011, 76 (20), 8232-8242. 11.

Douglass, I. B.; Evers, W. J., Methanesulfenyl Chloride. IV. The Reaction of

Sulfenyl Chlorides with Alkyl Xanthates and Trimethyl Thionophosphate. J. Chem. Soc. 1964, 29, 419-420. 12.

Dräger, M.; Gattow, G., Über Chalkogenocarbonate, XLVI. Darstellung und

Spektroskopische Eigenschaften Einiger Dimethyl Trichalkogenocarbonate. Chem. Ber. 1971, 104, 1429-1435. 13.

Minkwitz, R.; Neikes, F., Protonated O,S-Dimethyl Dithiocarbonate − Synthesis,

Spectroscopic Characterization and the Crystal Structure of (CH3O)(CH3S)CSH+SbF6−. Eur. J. Inorg. Chem. 2000, 2000 (10), 2283-2287. 14.

Juncal, L. C.; Cozzarín, M. V.; Romano, R. M., Conformational and

Spectroscopic Study of Xanthogen Ethyl Formates, ROC(S)SC(O)OCH2CH3. Isolation


27


Page 28 of 34

of CH3CH2OC(O)SH. Spectrochim Acta A Mol Biomol Spectrosc. 2015, 139 (0), 346355. 15.

Guimon, C.; Gonbeau, D.; Pfister-Guillouzo, G.; Åsbrink, L.; Sandström, J.,

Electronic Structure of Sulphur Compounds VI. Photoelectron Spectra of some Simple Thiocarbonyl Compounds. J. Electron Spectrosc. Rel. Phenom. 1974, 4 (1), 49-63. 16.

Holm, A.; Schroll, G., Mass Spectra of Some Simple O,S- and S,S-Dialkyl

Dithiocarbonates. Acta Chem. Scand. 1972, 26, 415-419. 17.

Thaddeus, P.; Guélin, M.; Linke, R. A., Three New "Nonterrestrial" Molecules.

Astrophys. J. 1981, 246, L41-L45. 18.

Margules, L.; Lewen, F.; Winnewisser, G.; Botschwina, P.; Müller, H. S. P., The

Rotational Spectrum up to 1 THz and the Molecular Structure of Thiomethylium, HCS+. Phys. Chem. Chem. Phys. 2003, 5, 2770-2773. 19.

Puzzarini, C., The HCS/HSC and HCS+/HSC+ Systems: Molecular Properties,

Isomerization, and Energetics. J. Chem. Phys. 2005, 123 (2), 024313. 20.

Agúndez, M.; Marcelino, N.; Cernicharo, J.; Tafalla, M., Detection of

Interstellar HCS and its Metastable Isomer HSC: New Pieces in the Puzzle of Sulfur Chemistry. A&A 2018, 611, 1-4. 21.

Buhl, D.; Snyder, L. E., Unidentified Interstellar Microwave Line. Nature 1970,

228, 267-269. 22.

Klemperer, W., Carrier of the Interstellar 8 9.190 GHz Line. Nature 1970, 227,

1230. 23.

Woods, R. C.; Dixon, T. A.; Saykally, R. J.; Szanto, P. G., Laboratory

Microwave Spectrum of HCO+. Phys. Rev. Lett. 1975, 35, 1269–1272.


28

Page 29 of 34 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


24.

Carrascosa, E.; Kainz, M. A.; Stei, M.; Wester, R., Preferential Isomer

Formation Observed in H3+ + CO by Crossed Beam Imaging. J. Phys. Chem. Lett. 2016, 7, 2742–2747. 25.

Herbst, E., The Astrochemistry of H3+. Philos. Trans. R. Soc. 2000, 358,

2523−2534. 26.

Herbst, E.; Klemperer, W., The Formation and Depletion of Molecules in Dense

Interstellar Clouds. Astrophys. J. 1973, 185, 505− 534. 27.

Geronés, M.; Erben, M. F.; Romano, R. M.; Cavasso Filho, R. L.; Della Védova,

C. O., Interstellar H3+ and HCS+ Ions Produced in the Dissociative Photoionization Process of CH3C(O)SCH3 in the Proximity of the Sulfur 2p, Carbon 1s, and Oxygen 1s Edges. J. Phys. Chem. A 2012, 116 (10), 2571-2582. 28.

Pilling, S.; Santos, A. C. F.; Boechat-Roberty, H. M., Photodissociation of

Organic Molecules in Star-Forming Regions II. Acetic Acid. Astron. Astrophys. 2006, 449, 1289-1296. 29.

Bava, Y. B.; Berrueta Martinez, Y.; Moreno Betancourt, A.; Erben, M. F.;

Cavasso Filho, R. L.; Della Védova, C. O.; Romano, R. M., Ionic Fragmentation Mechanisms of 2, 2, 2‐Trifluoroethanol Following Excitation with Synchrotron Radiation. ChemPhysChem 2015, 16, 322-330. 30.

Fantuzzi, F.; Pilling, S.; Santos, A. C. F.; Baptista, L.; Rocha, A. B.; Boechat-

Roberty, H. M., Photodissociation of Methyl Formate in Circumstellar Environment: Stability under Soft X-rays. Mon. Not. R. Astron. Soc. 2011, 407, 2631–2641. 31.

Pilling, S.; Boechat-Roberty, H. M.; Santos, A. C. F.; de Souza, G. G. B.; Naves

de Brito, A., Ionic yield and Dissociation Pathways from Soft X-ray Multi-ionization of Acetic Acid. J. Electron Spectrosc. Related Phenom. 2007, 156-158, 139-144.


29


32.

Page 30 of 34

Rodriguez Pirani, L.; Erben, M. F.; Boese, R.; Pozzi, C. G.; Fantoni, A. C.; Della

Vedova, C. O., Conformational Preference of Chlorothioformate Species: Molecular Structure of Ethyl Chlorothioformate, ClC(O)SCH2CH3, in the Solid Phase and NBO Analysis. Acta Crystallogr. 2011, B67 (4), 350-356. 33.

Rodríguez Pirani, L. S.; Geronés, M.; Della Védova, C. O.; Romano, R. M.;

Fantoni, A.; Cavasso-Filho, R.; Ma, C.; Ge, M.; Erben, M. F., Electronic Properties and Dissociative Photoionization of Thiocyanates. Part II. Valence and Shallow-Core (Sulfur and Chlorine 2p) Regions of Chloromethyl Thiocyanate, CH2ClSCN. J. Phys. Chem. A 2012, 116 (1), 231-241. 34.

Suoninen, E. J.; Thomas, T. D.; Anderson, S. E.; Runyan, M. T.; Ungier, L., An

XPS-AES Study of Gaseous Xanthates and Related Sulfur-Containing Compounds. J. Electron Spectrosc. Rel. Phenom. 1985, 35, 259-272. 35.

Lira, A. C.; Rodrigues, A. R. D.; Rosa, A.; Goncalves da Silva, C. E. T.;

Pardine, C.; Scorzato, C.; Wisnivesky, D.; Rafael, F.; Franco, G. S.; Tosin, G.; et. al., In First Year Operation of the Brazilian Source. European Particle Accelerator Conference, Stockholm. 1998, EPAC. 36.

Fonseca, P. T.; Pacheco, J. G.; Samogin, E.; Castro, A. R. B., Rev. Sci. Instr.

1992, 63, 1256-1259. 37.

Burmeister, F.; Coutinho, L. H.; Marinho, R. R. T.; Homem, M. G. P.; de

Morais, M. A. A.; Mocellin, A.; Björneholm, O.; Sorensen, S. L.; Fonseca, P. T.; Lindgren, et al., Description and Performance of an Electron-Ion Coincidence TOF Spectrometer Used at the Brazilian Synchrotron Facility LNLS J. Electron Spectrosc. Relat. Phenom. 2010, 180, 6-13. 38.

Kivimäki, A.; Ruiz, J. Á.; Erman, P.; Hatherly, P.; García, E. M.; Rachlew, E.;

Riu, J. R. i.; Stankiewicz, M., An Energy Resolved Electron–Ion Coincidence Study


30

Page 31 of 34 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


near the S 2p Thresholds of the SF6 Molecule J. Phys. B: At. Mol. Opt. Phys. 2003, 36, 781. 39.

Frasinski, L. J.; Stankiewicz, M.; Randall, K. J.; Hatherly, P. A.; Codling, K.,

Dissociative Photoionisation of Molecules Probed by Triple Coincidence; Double Timeof-Flight Techniques. J. Phys. B: At. Mol. Opt. Phys. 1986, 19, L819. 40.

Eland, J. H. D.; Wort, F. S.; Royds, R. N., A Photoelectron-Ion-Ion Triple

Coincidence Technique for the Study of Double Photoionization and its Consequences. J. Electron Spectrosc. Relat. Phenom. 1986, 41, 297-309. 41.

Naves de Brito, A.; Feifel, R.; Mocellin, A.; Machado, A. B.; Sundin, S.; Hjelte,

I.; Sorensen, S. L.; Björneholm, O., Femtosecond Dissociation Dynamics of CoreExcited Molecular Water. Chem. Phys. Lett. 1999, 309, 377-385. 42.

Laskin, J.; Lifshitz, C., Kinetic Energy Release Distributions in Mass

Spectrometry. J. Mass Spectrom. 2001, 36, 459-478. 43.

Simon, M.; LeBrun, T.; Morin, P.; Lavollée, M.; Maréchal, J. L., A

Photoelectron-Ion Multiple Coincidence Technique Applied to Core Ionization of Molecules. Nucl. Instr. and Meth. 1991, B62, 167-174. 44.

Santos, A. C. F.; Lucas, C. A.; de Souza, G. G. B., Dissociative Photoionization

of SiF4 around the Si 2p Edge: a New TOFMS Study with Improved Mass Resolution J. Electrón Spectrosc. Rel. Phenom. 2001, 114-116, 115-121. 45.

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;

Cheeseman, J. R.; Montgomery Jr., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; et. al., Gaussian 03. Revision B.04 ed., Gaussian, Inc., Pittsburgh PA 2003. 46.

Morini, F.; Knippenberg, S.; Deleuze, M. S.; Hajgato, B., Quantum Chemical

Study of Conformational Fingerprints in the Photoelectron Spectra and (e, 2e) Electron Momentum Distributions of n-Hexane. J. Phys. Chem. A 2010, 114 (12), 4400-4417.


31


47.

Page 32 of 34

Dunning, T. H. J., Gaussian Basis Sets for use in Correlated Molecular

Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90 (2), 1007-1023. 48.

Geronés, M.; Erben, M. F.; Ge, M.; Cavasso Filho, R. L.; Romano, R. M.; Della

Védova, C. O., Study of the Photodissociation Process of ClC(O)SCH3 Using both Synchrotron Radiation and HeI Photoelectron Spectroscopy in the Valence Region. J. Phys. Chem. A 2010, 114 (31), 8049-8055. 49.

Cortés, E.; Erben, M. F.; Geronés, M.; Romano, R. M.; Della Védova, C. O.,

Dissociative Photoionization of Methyl Thiocyanate, CH3SCN, in the Proximity of the Sulfur 2p Edge. J. Phys. Chem. A 2009, 113 (3), 564-572. 50.

Geronés, M.; Erben, M. F.; Romano, R. M.; Cavasso Filho, R. L.; Della Védova,

C. O., Evidence for the Formation of an Interstellar Species, HCS+, during the Ionic Fragmentation of Methyl Thiofluoroformate, FC(O)SCH3, in the 100-1000 eV Region. J. Phys. Chem. A 2010, 114 (46), 12353-12361.


32

Page 33 of 34

TOC Graphic 1.0

Io n Si g n al (u .a. )

VUV-Synchrotron radiation

0.8

3.0 CH3+ 2.5

HxCS

+

H

+

(x=0-3)

E= 173.8 eV

2.0

0.6 Counts (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 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4

E= 167.5 eV

1.5 S

+

CH3S

+

+

CH3OC(S)

E= 165.9 eV

1.0 +

HCO

0.2 160

OCS

+

SS

+

C(S)S

+

E= 164.4 eV

0.5

164

168

172

Photon Energy (eV)

176

180

HCS+

HCO+

C(S)SCH3+

CH3OC(S)SCH3+ E= 155.0 eV

0.0


0

20

40


100

120

140

33


254x190mm (96 x 96 DPI)


Page 34 of 34

Formation of HCO+ and HCS+ Ions in the Photodissociation of

Recommend Documents