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Wiens JP, Martinez O, Ard SG, Sweeny BC, Viggiano AA, Shuman NS. Kinetics of Cations with C 2 Hydrofluorocarbon Radicals. J Phys Chem A 2017; 121:8061-8068. [PMID: 28949143 DOI: 10.1021/acs.jpca.7b07778] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reactions of the cations Ar+, O2+, CO2+, and CF3+ with the C2 radicals C2H5, H2C2F3, C2F3, and C2F5 were investigated using the variable electron and neutral density attachment mass spectrometry technique in a flowing afterglow-Langmuir probe 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 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 rate coefficients that are generally elevated compared to those of stable species, ion-radical reactivity is generally decreased relative to that of reactions with stable species. In particular, long-range charge transfer appears more likely to be frustrated in the ion-radical systems.
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Affiliation(s)
- Justin P Wiens
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Oscar Martinez
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Shaun G Ard
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Brendan C Sweeny
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
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Wiens JP, Shuman NS, Miller TM, Viggiano AA. Mutual neutralization of He(+) with the anions Cl(-), Br(-), I(-), and SF6 (.). J Chem Phys 2016; 144:204309. [PMID: 27250308 DOI: 10.1063/1.4948637] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Mutual neutralization (MN) rate coefficients kMN for He(+) with the anions Cl(-), Br(-), I(-), and SF6 (-) are reported from 300 to 500 K. The measured rate coefficients may contain a contribution from transfer ionization, i.e., double ionization of the anion. The large rate coefficient for He(+) + SF6 (-) (2.4 × 10(-7) cm(3) s(-1) at 300 K) is consistent with earlier polyatomic MN results found to have a reduced mass dependence of μ(-1/2). Neutralization of He(+) by the atomic halides follows the trend observed earlier for Ne(+), Ar(+), Kr(+), and Xe(+) neutralized by atomic halides, kMN (Cl(-)) < kMN (Br(-)) < kMN (I(-)). Only an upper limit could be measured for the neutralization of He(+) by Cl(-). Predictions of the rate coefficients from a previously proposed simple model of atomic-atomic MN results are consistent with the present He(+)-halide rate coefficients. The temperature dependences are modestly negative for Br(-) and I(-), while that for SF6 (-) is small or negligible.
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Affiliation(s)
- Justin P Wiens
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Thomas M Miller
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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Shuman NS, Viggiano AA, Johnsen R. Flowing afterglow measurements of the density dependence of gas-phase ion-ion mutual neutralization reactions. J Chem Phys 2013; 138:204302. [PMID: 23742470 DOI: 10.1063/1.4803159] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have studied the dependence of several ion-ion mutual neutralization (MN) reactions on helium density in the range from 1.6 × 10(16) to 1.5 × 10(17) cm(-3) at 300 K, using the Variable Electron and Neutral Density Attachment Mass Spectrometry method. The rate coefficients of the reactions Ar(+) + Br2(-), Ar(+) + SF6(-), and Ar(+) + C7F14(-) were found to be independent of gas density over the range studied, in disagreement with earlier observations that similar MN reactions are strongly enhanced at the same gas densities. The cause of the previous enhancement with density is traced to the use of "orbital-motion-limit" theory to infer ion densities from the currents collected by ion-attracting Langmuir probes in a region where it is not applicable.
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Affiliation(s)
- Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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Fournier JA, Shuman NS, Melko JJ, Ard SG, Viggiano AA. A novel technique for measurement of thermal rate constants and temperature dependences of dissociative recombination: CO2(+), CF3(+), N2O(+), C7H8(+), C7H7(+), C6H6(+), C6H5(+), C5H6(+), C4H4(+), and C3H3(+). J Chem Phys 2013; 138:154201. [PMID: 23614415 DOI: 10.1063/1.4801657] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A novel technique using a flowing afterglow-Langmuir probe apparatus for measurement of temperature dependences of rate constants for dissociative recombination (DR) is presented. Low (~10(11) cm(-3)) concentrations of a neutral precursor are added to a noble gas∕electron afterglow plasma thermalized at 300-500 K. Charge exchange yields one or many cation species, each of which may undergo DR. Relative ion concentrations are monitored at a fixed reaction time while the initial plasma density is varied between 10(9) and 10(10) cm(-3). Modeling of the decrease in concentration of each cation relative to the non-recombining noble gas cation yields the rate constant for DR. The technique is applied to several species (O2(+), CO2(+), CF3(+), N2O(+)) with previously determined 300 K values, showing excellent agreement. The measurements of those species are extended to 500 K, with good agreement to literature values where they exist. Measurements are also made for a range of CnHm(+) (C7H7(+), C7H8(+), C5H6(+), C4H4(+), C6H5(+), C3H3(+), and C6H6(+)) derived from benzene and toluene neutral precursors. CnHm(+) DR rate constants vary from 8-12 × 10(-7) cm(3) s(-1) at 300 K with temperature dependences of approximately T(-0.7). Where prior measurements exist these results are in agreement, with the exception of C3H3(+) where the present results disagree with a previously reported flat temperature dependence.
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Affiliation(s)
- Joseph A Fournier
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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Miller TM, Friedman JF, Shuman NS, Ard SG, Melko JJ, Viggiano AA. Electron attachment to C7F14, thermal detachment from C7F14(-), the electron affinity of C7F14, and neutralization of C7F14(-) by Ar+. J Phys Chem A 2012; 116:10293-300. [PMID: 23030828 DOI: 10.1021/jp306843a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rate coefficients and branching fractions have been measured for electron attachment to perfluoromethylcyclohexane, C(7)F(14), along with thermal detachment rate coefficients for C(7)F(14)(-), from 300 to 630 K, using a flowing-afterglow Langmuir-probe apparatus. The attachment rate coefficient at room temperature is 4.5 ± 1.2 × 10(-8) cm(3) s(-1) and increases with temperature at a rate described by an activation energy of 50 ± 25 meV. Thermal electron detachment is negligible at room temperature, but measurable at 600 K and above, reaching 2300 ± 1300 s(-1) at 630 K. Analysis of the attachment-detachment equilibrium yields EA(C(7)F(14)) = 1.02 ± 0.06 eV, in agreement with the literature value while more than halving the uncertainty. Implications of the measurement for the electron affinity of SF(6) are discussed. The dominant product of electron attachment is the parent anion, but C(6)F(11)(-) and C(7)F(13)(-) are also observed at very low levels (<0.1%) at room temperature and increase in importance as the temperature is increased, reaching ~10% each at 630 K. In the course of this work we have also measured rate coefficients for the neutralization of C(7)F(14)(-) by Ar(+) at 300, 400, and 500 K: 4.8, 3.5, and 3.1 × 10(-8) cm(3) s(-1), respectively, with uncertainties of ±5 × 10(-9) cm(3) s(-1).
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Affiliation(s)
- Thomas M Miller
- Space Vehicles Directorate, Air Force Research Laboratory, Kirtland AFB, New Mexico 87117-5776, USA
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Shuman NS, Miller TM, Friedman JF, Viggiano AA. Electron Attachment to Fe(CO)n (n = 0–5). J Phys Chem A 2012; 117:1102-9. [DOI: 10.1021/jp304480x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nicholas S. Shuman
- Space Vehicles
Directorate, Air Force Research Laboratory, Kirtland Air Force Base, New Mexico
87117-5776, United States
| | - Thomas M. Miller
- Space Vehicles
Directorate, Air Force Research Laboratory, Kirtland Air Force Base, New Mexico
87117-5776, United States
| | - Jeffrey F. Friedman
- Space Vehicles
Directorate, Air Force Research Laboratory, Kirtland Air Force Base, New Mexico
87117-5776, United States
| | - Albert A. Viggiano
- Space Vehicles
Directorate, Air Force Research Laboratory, Kirtland Air Force Base, New Mexico
87117-5776, United States
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Haughey SA, Field TA, Langer J, Shuman NS, Miller TM, Friedman JF, Viggiano AA. Dissociative electron attachment to C2F5 radicals. J Chem Phys 2012; 137:054310. [DOI: 10.1063/1.4738759] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Miller TM, Shuman NS, Viggiano AA. Behavior of rate coefficients for ion-ion mutual neutralization, 300–550 K. J Chem Phys 2012; 136:204306. [DOI: 10.1063/1.4720499] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
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Shuman NS, Miller TM, Friedman JF, Viggiano AA, Maeda S, Morokuma K. Temperature dependences of rate coefficients for electron catalyzed mutual neutralization. J Chem Phys 2011; 135:024204. [DOI: 10.1063/1.3605631] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Affiliation(s)
- Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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