Kinetics of Cations with C2 Hydrofluorocarbon Radicals - The Journal

Subscriber access provided by UNIV OF UTAH

Article 2

Kinetics of Cations With C Hydrofluorocarbon Radicals Justin P. Wiens, Oscar Martinez, Shaun G Ard, Brendan C Sweeny, Albert A Viggiano, and Nicholas S. Shuman J. Phys. Chem. A, Just Accepted Manuscript • Publication Date (Web): 26 Sep 2017 Downloaded from http://pubs.acs.org on September 26, 2017

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 31

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

Kinetics of Cations with C2 Hydrofluorocarbon Radicals Justin P. Wiens,1 Oscar Martinez Jr., Shaun G. Ard, Brendan C. Sweeny, Albert A. Viggiano, and Nicholas S. Shuman* Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, NM 87117,USA * Corresponding author; e-mail: [email protected] 1

Present address: Central New Mexico Community College, 525 Buena Vista SE, Albuquerque, NM 87106, USA

Abstract Reactions of the cations Ar+, O2+, CO2+, and CF3+ with the C2 radicals C2H5, H2C2F3, C2F3, and C2F5 have been investigated using the Variable Electron and Neutral Density Attachment Mass Spectrometry (VENDAMS) technique in a flowing afterglow–Langmuir Probe (FALP) apparatus at room temperature. Rate coefficients for observed product channels for these 16 reactions are reported, as well as rate coefficients and product branching fractions for the 16 reactions of the same cations with each of the stable neutrals used as radical precursors (the species RI, where R is the radical studied). Reactions with the stable neutrals proceed by charge transfer at or near the collisional rate coefficient where energetically allowed; where charge

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

transfer is endothermic, bond-breaking/bond-making chemistry occurs. While also efficient, reactions with the radicals are more likely to occur at a smaller fraction of the collisional rate coefficient, and bond-breaking/bond-making chemistry occurs even in some cases where charge transfer is exothermic. It is noted that unlike radical reactions with neutral species, which occur with generally elevated rate coefficients compared to stable species, ion-radical reactivity is generally decreased relative to reactions with stable species. In particular, long-range charge transfer appears more likely to be frustrated in the ion-radical systems.

Introduction Weakly ionized plasma environments generally contain concentrations of transient species, e.g. small fluorocarbon radicals in a discharge through fluoromethane. The chemical behavior of many possible reactions of these species has not been quantified, limiting the scope of processes that can be understood in detail. A more complete understanding of plasma-assisted combustion1, 2 and of plasma etching3 requires knowledge of the kinetics and dynamics of many different species, including closed- and open-shell neutrals and ions. Additionally, such reactions are relevant to chemical ionization mass spectrometry methods and, at low temperatures, to modeling of the interstellar medium. Plasma reactions of most open-shell neutrals are difficult to study because of their inherent reactivity. To date, only a handful of studies have explored the kinetics and dynamics of ion–polyatomic radical systems. A popular method for hydrocarbon radical production is cracking of the closed-shell precursors via pyrolysis in a Chen-type nozzle.4 Zhang et al.5 reacted polyatomic hydrocarbon radicals with H3O+ and OH– in a selected-ion flow tube (SIFT), identifying product branching, although direct


Page 2 of 31

Page 3 of 31

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


rate measurements were difficult. The Gross group6 reacted allyl and allene with the benzene cation, as well as allyl cation with benzene, using ion cyclotron resonance (ICR). Again multiple products could be detected, but the kinetics were not explored. Most recently, the Farrar group elucidated mechanistic details and product channels for H3+ + CH3 and C+ (2P) + C3H5 (allyl radical) in a velocity-map imaging molecular beam apparatus, an important step in understanding the dynamics of ion–radical systems.7, 8 We have measured the kinetics of electron–radical processes9-14 and several cation reactions with the CF3,15 CH3,16 and hydrofluorocarbon radicals.17 That work was an extension of the Variable Electron and Neutral Density Attachment Mass Spectrometry (VENDAMS) technique developed in our laboratory.12 In VENDAMS, radicals are generated through dissociative electron attachment to stable molecules rather than through pyrolysis or discharge. Because the neutral and electron concentrations are known, the radical concentration of the neutral remaining after attachment can be determined within 10-20%. However, the concentrations are low – on the order of ~109-1010 cm-3. The chemistry is determined by monitoring the relative ion composition as a function of the initial plasma density and fitting those measurements through modeling of the (generally complicated) kinetics occurring in the flow tube. VENDAMS offers a moderately generalizable method of studying the kinetics of these difficult-to-access reactions. Here we expand on previous work involving methyl-like radicals with studies of C2 hydro-, fluoro-, and hydrofluorocarbon radicals reacting with a variety of easily produced cations. Measurement of each radical reaction requires also kinetic measurements of the cation with the stable neutral used as a precursor to the radical (in the case of each radical species R studied here, the precursor species is RI), providing a natural data set 3 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

for comparison with the radical reactions, looking for general distinctions between the radical reactivity and that of closed-shell species.

Experimental The flowing afterglow–Langmuir probe (FALP) apparatus18 and VENDAMS method have been described in detail previously.12, 19 The FALP consists of a 1-m long, 7 cm dia. stainless steel-lined glass flow tube containing a microwave discharge cavity on a 2.5 cm diameter arm at the upstream end. Approximately 13 std. L min-1 helium buffer gas (99.999%, Matheson) was passed through a Micro Torr® filter (SAES Pure Gas, Inc.) in series with zeolite traps at liquid nitrogen temperature, then discharged inside the microwave cavity to create a weakly ionized plasma comprised primarily of He+, He2+, metastable He*, and electrons. Argon (99.999%, Matheson) was added a few cm downstream at 0.2 std. L min-1, converting He2+ and He* to Ar+. Less than 5 percent of the positive charge in the plasma is composed of He+ or other ions arising from charge exchange to air and water impurities. All flows were metered using mass flow controllers (MKS). The electron density along the center axis of the flow tube was measured using a moveable Langmuir probe, a 0.025 mm diameter x 7 mm long tungsten wire. Typical pressure in the flow tube was 1.5 Torr. Under this condition, ion velocity (measured by pulsing the microwave discharge and monitoring arrival time of the disturbance at the Langmuir probe as a function of distance along the flow tube) was 60 m s-1. The rate of ambipolar diffusion was measured by monitoring the electron density decay of the nascent plasma as a function of time using the moveable Langmuir probe. A gas inlet comprising six glass needles evenly spaced radially on a 2 cm radius from the center of the flow tube allowed for addition of


Page 4 of 31

Page 5 of 31

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


reactant gases 44 cm prior to the terminus of the flow tube. The flow tube terminates in a truncated nosecone, with the core of the flow sampled through a 0.3 mm aperture into a high vacuum region. The ions were transported using a rectilinear RF ion guide to the entrance of an orthogonally-accelerated reflectron time-of-flight mass spectrometer and detected using two microchannel plates in a chevron configuration. The experiments here require production of both particular cation and radical species. Reactions of Ar+ use the nascent plasma produced as described above. Reactions of O2+, CO2+, and CF3+ further modify that plasma by addition of a reactant (O2, CO2, CF4) through the glass reactant inlet in concentrations sufficient to convert most Ar+ within ~1 ms, namely ~5×1012 cm-3 for CO2 and CF4, and ~5×1013 cm-3 for O2. Radical species (C2F3, C2F5, CF3CH2, C2H5) are produced by addition of precursors that rapidly undergo dissociative electron attachment, namely C2F3I, C2F5I, CF3CH2 I, C2H5I. Each of these species RI proceeds by RI + e- R + I-

(1)

with a rate coefficient either drawn from the literature or measured by the standard technique of monitoring the electron density decay as a function of time using the moveable Langmuir probe (Table 1). 20 For the VENDAMS experiments, the radical precursor gases are added through the same reactant inlet as the charge transfer reactants (the gases merged on the low pressure sides of the mass flow controllers). However, due to the fact that the rate coefficient of (1) is 500-5000 times that of the charge transfer reactions with Ar+, RI is added only at concentrations of ~1010 cm-3. Table 1. Thermal electron attachment rate coefficients for the indicated species at 300 K. Uncertainty is ±25%. k (×10-7 cm3 s-1) 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

C2F3I C2F5I CF3CH2I C2H5I a from ref. 21

1.5 a 1.5a 2.8 0.13a

Analysis of the VENDAMS data to determine cation-radical kinetics requires kinetic data on other reactions inevitably occurring in the flow tube. These include the reaction rate coefficient and product branching of each cation with the radical precursor, the electron attachment rate coefficient of the radical precursor, and mutual neutralization rate coefficients of product cations I-, the dominant anion present in these experiments. Kinetics of the cationradical precursor reactions are measured by standard methods both using the FALP apparatus described above as well as using a SIFT apparatus described elsewhere.22 Mutual neutralization rate coefficients are taken from the literature or estimated as described elsewhere.23-25 The VENDAMS measurements are made by monitoring the relative ion densities after a fixed reaction time (distance) as a function of the plasma density at the reactant inlet, [e] 0. The plasma density is determined by measuring the absolute electron density using the Langmuir probe,26 stationed 1 cm upstream of the inlet. This initial density is variable from ~108 cm-3 (the lower limit reliably measured using the Langmuir probe) to ~2 x 1010 cm-3, controlled primarily by translating the microwave source further from or closer to the inlet. A schematic of the FALP apparatus and illustration of the VENDAMS technique to measure ion-radical kinetics appears in Figure 1. The modeled ion concentrations are also shown in the figure. As can be seen, both Ar+ and e- are largely converted to other species in about 1 ms, resulting in a plasma dominated by a single cation (e.g. O2+) and I-.


Page 6 of 31

Page 7 of 31

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 1. Schematic of the FALP apparatus and a VENDAMS measurement of the kinetics of O2+ + C2F5. Modeled concentrations of charged species are shown as both a function of reaction time relative to addition of the O2 and C2F5I reactants and position along the flow tube.

Data Analysis and Results A detailed discussion of using the VENDAMS technique to determine cation-radical kinetics has been presented elsewhere;15 a relatively brief description follows here. A radical of interest is prepared in the afterglow by dissociative electron attachment to a precursor molecule, i.e. reaction (1). The afterglow is also prepared with a dominant cation, which reacts with both the precursor molecule (the ‘primary’ reaction) and the radical species (the ‘secondary’ reaction). Relative product ion abundances are measured as a function of initial plasma density, [e] 0. At low [e] 0, the primary reaction dominates, and the relative abundances reflect the kinetics (rate coefficient and product branching fractions) of that reaction (Figure 2). As [e] 0 increases, the rate of reaction (1) increases, increasing the concentration of both the radical and anion species, 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

leading both to an increasing contribution of the secondary reaction as well as to mutual neutralization of all cations with I-. As a result, relative abundances of products of the primary reaction decrease with increasing [e] 0, while products of the secondary reaction increase. Qualitatively, the shape of the curves in Figure 2 reflect the series of reactions forming that cation (e.g. primary products will have a negative slope, secondary products a positive slope, and higher-order products an even more positive slope), while the magnitude of the relative abundances reflect the magnitude of the rate coefficients of those processes. Deriving quantitative information from the data requires modeling the kinetics of all relevant processes occurring in the afterglow throughout the known reaction time.


Page 8 of 31

0.8 0.6 0.4 0.2 0.0 0

1

50

8 6

O2

100

150 200 Mass (Da)

250

300

+

4 2

Relative abundance

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


Abundance (a.u.)

Page 9 of 31

0.1

8 6

C2F5I

+

C2F5+

4

C2F4I

+

2

0.01

8 6

CF3+

4 2

I

+

0.001 10

9

2

3

4

5

6 -3

7 8 9

10

10

2

[e]0 (cm )

Figure 2. Representative mass spectra (top) and corresponding relative ion abundances (bottom) as a function of initial plasma density [e] 0 for VENDAMS measurements of the O2+ + C2F5 reaction. Ions abundances (solid points) and best fits from modeling (solid lines) resulting from ancillary processes are shown in grey. Solid green line indicates best fit C2F5+ abundance, with modeled contributions from O2+ + C2F5I (dashed green line) and from O2+ + C2F5 (dotted green line) indicated separately. Dashed blue lines indicate modeled fits at the uncertainty limits for the rate coefficient of O2+ + C2F5 CF3+ + CF2 + O2. Mass spectra are shown from lowest (front) to highest (back) [e] 0 along the z-axis.



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 data shown in Figure 2 for the reaction of O2+ + C2F5 is typical of the data in this work, neither the most nor the least well-defined. Modeled fits are in generally good agreement with the experimental data. The mass spectra generally contain minor peaks due to processes occurring in the afterglow in parallel to those of interest, e.g. H2O+ arising from charge exchange of the primary cation with water present in the flow tube in low concentrations (< ~1010 cm-3). The presence of such species in small concentrations have been determined to have a negligible effect on the derived kinetics. Unlike standard measurements of ion-molecule kinetics where a total rate coefficient is determined by the disappearance of the reactant ion, here partial rate coefficients of ion-radical reaction channels are determined from the appearance of product ions. In some cases, ions are produced only through the secondary reaction, resulting in an unambiguous signal and welldetermined partial rate coefficient for that process. In other cases, an ion may be produced by both the primary and secondary reactions, for instance the C2F5+ product in Figure 2. In these cases, the contributions of the two channels must be deconvoluted during modeling, resulting in larger uncertainties in the derived rate coefficients. In some cases the primary product ion signal may entirely obscure that from the secondary reaction, and only an upper limit on the secondary partial rate coefficient may be determined. In all cases, the kinetics of the primary reaction must be known. Those kinetics are determined here through standard techniques using both the FALP apparatus and a selected ion flow tube apparatus; measurements using the different apparatuses were in agreement.27 Representative data for O2+ + C2F5I, the primary reaction corresponding to the VENDAMS data in Figure 2, is shown in Figure 3. Uncertainties in these measurements are dominated by systematic uncertainties in the flow tube pressure and reactant flow rates, and are


Page 10 of 31

Page 11 of 31

typically ~25%. Experimental conditions of and the reaction scheme used to model the data in

Abundance (a.u.)

both Figures 2 and 3 are provided in Supporting Information.

0.8 0.6 0.4 0.2 0.0 0

1

8 6 4 2

Abundance (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


0.1

0.01

50

O2

100

150 200 Mass (Da)

250

300

+

C2F5I

+

8 6 4

C2F5

2

C2F4I

+

+

8 6 4

C3F5

+

2

0.2

0.4

0.6

0.8

1.0 -3

1.2 1.4x1011

[C2F5I] (cm )

Figure 3. Representative mass spectra (top) and corresponding relative ion abundances (solid points, bottom) as a function of reactant concentration for the O2+ + C2F5I reaction. Solid lines are best-fit modeling of the data; dashed lines are modeling at the uncertainty limits of the measured rate coefficients. Mass spectra are shown from lowest (front) to highest (back) neutral concentration along the z-axis.



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

As described elsewhere,12 rate coefficients are determined from the VENDAMS data by minimizing the weighted least squares difference between the experimental product ion abundances and those calculated by kinetic modeling (i.e. iteratively solving the set of coupled differential equations describing the chemical reactions occurring in the afterglow, from the known initial conditions and throughout the known reaction time). Relevant parameters (rate coefficients, initial concentrations, mass discrimination) are varied in a Monte Carlo manner over ranges defined by the uncertainty in those values. Where no literature information exists, rate coefficients are varied over a range limited by the calculated collisional rate coefficient.28 The largest contribution to the uncertainties in the determined rate coefficients is generally the uncertainty in the modeled fit (as opposed to systematic uncertainties in the experiment). Uncertainties in each rate coefficient are individually determined by inspecting the change in the weighted-least squares fit as a function of that rate coefficient, and vary widely, but are typically between 25% - 75%. At the thermal energies of these experiments, reactions that are endothermic to any significant extent will not occur. Identifying which reaction channels are exothermic, and therefore possible, aids interpretation of the VENDAMS data. Unfortunately, no experimental or calculated thermochemistry exists for many of the fluoro- and iodo-containing radicals and ions relevant to these systems. Because the number of species with undetermined thermochemistry is large and only coarse accuracy is required in most cases to determine whether a channel is energetically accessible or not, we calculate the needed enthalpies of formation using density functional theory, with results available in Supporting Information. Measured ion-molecule and ion-radical rate coefficients are presented in Tables 2-9, along with collision rates calculated using the parameterization of Su and Chesnavich.28 12 ACS Paragon Plus Environment

Page 12 of 31

Page 13 of 31

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


Table 2. Rate coefficients (10-10 cm3 s-1) for reactions with C2F3I. Reaction kpartial ∆Hr,298K (kJ mol-1) Ar+ + C2F3I→ C2F3I+ + Ar 1 ±0.5 -624 + → C2F3 + I + Ar 1 ±0.5 -274 + → CFI + CF2 + Ar 5 ±2 -264 + → I + C2F3 + Ar 1 ±0.5 -250 + → C2F2I + F + Ar 7 ±2 -211 → CF+ + CF2 + Ar 2 ±1 6 + + CO2 + C2F3I→ C2F3I + CO2 4 ±2 -432 + → C2F3 + I + CO2 0.7 ±0.5 -83 + → CFI + CF2 + CO2 11 ±3 -72 + → CF2I + CF + CO2 1 ±0.5 -69 + → C2F2I + F + CO2 1 ±0.5 -20 O2+ + C2F3I → C2F3I+ + O2 18 ±5 -268 CF3+ + C2F3I → C2F3I+ + CF3 1 ±0.5 19 + → C2F2I + CF4 9 ±2 -113 + → CF2I + C2F4 0.5 ±0.5 -72 → I+ + C3F6 1 ±0.5 -47 Table 3. Rate coefficients (10-10 cm3 s-1) for reactions with C2F5I. Reaction kpartial ∆Hr,298K (kJ mol-1) Ar+ + C2F5I→ CF2I+ + CF3 + Ar 0.8 ±0.5 -376 + → I + C2F5 + Ar 1 ±0.5 -297 + → CF3 + CF2I + Ar 2 ±1 -296 → C2F4I+ + F + Ar 6 ±2 -199 + + CO2 + C2F5I→ CFI + CF4 + CO2 0.8 ±0.5 -212 + → C2F5 + I + CO2 8 ±2 -186 + → I + C2F5 + CO2 1 ±0.5 -105 → C2F4I+ + F + CO2 1.5 ±0.5 -8 + + O2 + C2F5I→ C2F5I + O2 9 ±2 -143 + → C2F5 + O2 3 ±2 -21 + + CF3 + C2F5I→ C2F4I + CF4 6 ±2 -101 Table 4. Rate coefficients (10-10 cm3 s-1) for reactions with CF3CH2I. Reaction kpartial ∆Hr,298K (kJ mol-1) Ar+ + CF3CH2I→ CH2I+ + CF3 + Ar 1 ±0.5 -379 + →CF2CH2I + F + Ar 7 ±2 -330 + → I + CF3CH2 + Ar 2 ±1 -291 + → CF3 + CF2I + Ar 2 ±1 -109 + → CFH2 + CF2I + Ar 3 ±1 -77 13 ACS Paragon Plus Environment

ktot

kcollision

17 ± 4

14

18 ± 5

14

18 ± 5

16

11 ± 3

11

ktot

kcollision

10 ± 3

14

11 ± 3

14

12 ± 3

15

6±2

11

ktot

kcollision

15 ± 3

19


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

CO2+ + CF3CH2I→ CF3CH2I+ + CO2 → CH2FCF2+ + I + CO2 → CF2CH2+ + IF + CO2 → CH2I+ + CF3 + CO2 → CF2CH2I+ + F + CO2 → I+ + CF3CH2F + CO2 O2+ + CF3CH2I→ CF3CH2I+ + O2 → CH2FCF2+ + I + O2 → CF2CH2+ + IF + O2 → CH2I+ + CF3 + O2 → CF2CH2I+ + F + O2 CF3+ + CF3CH2I→ CF2CH2I+ + CF4

2 ±1 10 ±3 3 ±1 2 ±1 1 ±0.5 3 ±1 13 ±3 2 ±1 0.7 ±0.5 0.7 ±0.5 1 ±0.5 17 ±3

Page 14 of 31

-359 -282 -199 -187 -139 -99 -195 -117 -35 -23 25 -232

Table 5. Rate coefficients (10-10 cm3 s-1) for reactions with C2H5I. Reaction kpartial ∆Hr,298K (kJ mol-1) Ar+ + C2H5I→ C2H3+ + H2 + I + Ar 11 ±3 -290 + →I + C2H5 + Ar 6 ±2 -278 + + CO2 + C2H5I→ C2H5I + CO2 5 ±2 -410 + → C2H5 + I + CO2 8 ±2 -312 → C2H3+ + I + H2 + CO2 2 ±1 -99 + → I + C2H5 + CO2 1 ±0.5 -86 + + O2 + C2H5I→ C2H5I + O2 9 ±2 -246 + → C2H5 + I + O2 5 ±2 -147 + → C2H3 + H2 + I + O2 2 ±1 -70 + + CF3 + C2H5I→ C2H5 + CF3I 11 ±3 -90 Table 6. Rate coefficients (10-10 cm3 s-1) for reactions with C2F3. Reaction kpartial ∆Hr,298K (kJ mol-1) -537 1 +−20.5 Ar+ + C2F3→ C2F3+ + Ar → CF+ + CF2 + Ar → CF2+ + CF + Ar → C2F2+ + F + Ar + CO2 + C2F3 → C2F3+ + CO2 → C2F3O+ + CO O2+ + C2F3 → CF3+ + CO2 → C2F3O+ + O → CF+ + CF2 + O2 CF3+ + C2F3 → C2F4+ + CF2 + Ar

2 ± 1.5 0.5 ± 0.4 2.5 ± 1.5 0.3 ± 0.2 1.3 ± 0.7 6±2 2±1

Kinetics of Cations with C2 Hydrofluorocarbon Radicals - The Journal

Recommend Documents