Rate constants and vibrational distributions for water‐forming reactions of OH and OD radicals with thioacetic acid, 1,2‐ethanedithiol and tert‐butanethiol

Abstract

Reactions of OH and OD radicals with CH3C(O)SH, HSCH2CH2SH, and (CH3)3CSH were studied at 298 K in a fast‐flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10−11 cm3 molecule−1 s−1 for the OD + CH3C(O)SH reaction and (3.8 ± 0.7) × 10−11 cm3 molecule−1 s−1 for the OD + HSCH2CH2SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H2S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C2H5)2S reference reaction, the rate constant for the OD + (CH3)3CSH reaction was estimated to be (3.6 ± 0.7) × 10−11 cm3 molecule−1 s−1. Vibrational distributions of the H2O and HOD molecules from the title reactions are typical for H‐atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.

Reactions of OH and OD radicals with simple thiols and sulfides studied by infrared chemiluminescence of isotopic water products: Reaction OH + CH3SH revisited

“…The S‐H BDEs in CH 3 C(O)SH and (CH 3 ) 3 CSH are similar to that in methanethiol, 18 hence, abstraction from S‐atom is expected to produce similar vibrational excitation of the water product. The CH 3 groups are bound to a carbon atom, which increases the D(C‐H) values and reduces the branching fraction for H‐atom abstraction from the methyl group relative to CH 3 SH.…”

“…The surprisal parameters and results for energy disposal are presented below. The changes in energy disposal parameters from the previous analysis 18 are minor.…”

“…34–36) and < E av > = 33.9 kcal mol −1 was assigned to the major channel of both reactions. The spectra 18 from reactions (4) and (5) were refitted using the new model bands and the distributions were analyzed neglecting channel (b). Simulation and surprisal analysis are given in the Supporting Information.…”

“…Since the rate constant for the OH + CH 3 C(O)SH reaction is k 4a + k 4b = 1.3 × 10 −11 cm 3 molecule −1 s −1 (Ref. 18), branching fraction of ∼6% corresponds to k 4b ≈ 7.8 × 10 −13 cm 3 molecule −1 s −1 , which gives the rate constant per H‐atom k 4b (H) ≈ 2.6 × 10 −13 cm 3 molecule −1 s −1 . This value is close to the k (H) for the OH reactions with n‐butane, iso‐butane, n‐pentane, and n‐hexane, 38 in which C‐H BDE is 98‐100 kcal mol −1 .…”

“…In this paper, we present revised overall vibrational distributions for H 2 O and HOD from OH(OD) reactions with CH 3 SH, CH 3 C(O)SH, and (CH 3 ) 3 CSH 18 . These results illustrate changes in the H 2 O and HOD vibrational distributions from these reactions, but the basic interpretations 4 are unchanged.…”