Mutual neutralization of atomic rare-gas cations (Ne+, Ar+, Kr+, Xe+) with atomic halide anions (Cl−, Br−, I−)

Abstract

We report thermal rate coefficients for 12 reactions of rare gas cations (Ne(+), Ar(+), Kr(+), Xe(+)) with halide anions (Cl(-), Br(-), I(-)), comprising both mutual neutralization (MN) and transfer ionization. No rate coefficients have been previously reported for these reactions; however, the development of the Variable Electron and Neutral Density Attachment Mass Spectrometry technique makes it possible to measure the difference of the rate coefficients for pairs of parallel reactions in a Flowing Afterglow-Langmuir Probe apparatus. Measurements of 18 such combinations of competing reaction pairs yield an over-determined data set from which a consistent set of rate coefficients of the 12 MN reactions can be deduced. Unlike rate coefficients of MN reactions involving at least one polyatomic ion, which vary by at most a factor of ∼3, those of the atom-atom reactions vary by at least a factor 60 depending on the species. It is found that the rate coefficients involving light rare-gas ions are larger than those for the heavier rare-gas ions, but the opposite trend is observed in the progression from Cl(-) to I(-). The largest rate coefficient is 6.5 × 10(-8) cm(3) s(-1) for Ne(+) with I(-). Rate coefficients for Ar(+), Kr(+), and Xe(+) reacting with Br2 (-) are also reported.

Dissociative recombination and mutual neutralization of heavier molecular ions: C10H8+, WF5+, and CnFm+

“…28 Although TI of several C n F m + cations with I − would be exothermic, we saw no evidence of this pathway. …”

“…For MN of Br − and I − , the previously measured values for Ar + /Br − and Ar + /I − were used. 28 To determine the rate coefficient for the reaction of interest, the set of all exothermic reactions of species known or inferred to be present in the flow tube is first identified. Concentrations of the species are determined by iteratively solving the set of coupled differential equations describing the reaction system throughout the known reaction time, subject to the set of rate constants k i for these reactions and the measured ambipolar diffusion rate.…”

“…VEN-DAMS has yielded DR and MN results for a number of systems. 4,[27][28][29] Most recently, our group reported thermal MN rate coefficients for many polyatomic cations with the halide anions Cl − , Br − , and I − . 29 Here, we extend that work with MN and DR measurements for cations originating from three larger molecules: perfluoro(methylcyclo)hexane [CF 3 (c-C 6 F 11 ), denoted by C 7 F 14 ], WF 6 , and naphthalene (C 10 H 8 ).…”

Kinetics of Cations with C2 Hydrofluorocarbon Radicals

“…Kinetics of the cation–radical precursor reactions are measured by standard methods both using the FALP apparatus described above as well as using a SIFT apparatus described elsewhere . Mutual neutralization rate coefficients are taken from the literature or estimated as described elsewhere. − …”

Mutual neutralisation of O+ with O−: investigation of the role of metastable ions in a combined experimental and theoretical study

“…Flowing Afterglow -Langmuir Probe (FALP). [15][16][17][18][19][20][21] Data are obtained under thermal 300-600 K conditions, and report several interesting conclusions: systems of four or more atoms react with very similar rate constants and triatomic systems somewhat slower, 16 while atom-atom systems proceed with widely varying rate constants. However, only under rare circumstances can the product distributions be measured and no information on the states of these products can be obtained.…”