The Hydrogen Abstraction Reaction H₂S + OH → H₂O + SH: Convergent Quantum Mechanical Predictions

Abstract

The hydrogen abstraction reaction HS + OH → HO + SH has been studied using the "gold standard" CCSD(T) method along with the Dunning's aug-cc-pVXZ (up to 5Z) basis sets. For the reactant (entrance) complex, the CCSD(T) method predicts a HSH···OH hydrogen-bonded structure to be lowest-lying, and the other lower-lying isomers, including the two-center three-electron hemibonded structure HS···OH, have energies within 2 kcal/mol. The similar situation is for the product (exit) complex. With the aug-cc-pV5Z single point energies at the aug-cc-pVQZ geometry, the dissociation energy for the reactant complex to the reactants (HS + OH) is predicted to be 3.37 kcal/mol, and that for the product complex to the products (HO + SH) is 2.92 kcal/mol. At the same level of theory, the classical barrier height is predicted to be only 0.11 kcal/mol. Thus, the OH radical will react promptly with HS in the atmosphere. We have also tested the performance of 29 density functional theory (DFT) methods for this reaction. Most of them can reasonably predict the reaction energy, but the different functional give quite different energy barriers, ranged from -10.3 to +2.8 kcal/mol, suggesting some caution in choosing density functionals to explore the PES of chemical reactions.

Weak Interactions in Interstellar Chemistry: How Do Open Shell Molecules Interact with Closed Shell Molecules?

“…The OH radical was detected in the ISM more than 5 decades ago, in 1964 . Besides astrochemistry, it is also important in combustion chemistry. − Hence, a variety of studies featuring the interaction of the OH radical, especially with H 2 O, have been reported earlier. − The geometries and interaction energies obtained in this work are very much similar to earlier results obtained, thereby validating the present work.…”

“…Some studies featuring potential energy surfaces of some interstellar/astrochemical gas-phase chemical reactions usually report a pre-reactant complex, which facilitates further reaction. Such studies have especially been performed with the OH radical, − because it is relevant in not just astrochemistry but also combustion chemistry. The pre-reactant complex in the case of OH radicals is held together by weak chemical interactions, mainly hydrogen bonding.…”

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

“…The energy disposal pattern with about 50% of reaction energy released as H 2 O and HOD vibrations supports such mechanism. Partitioning of energy differs from that for the OH reaction with H 2 S, although all the reactions are presumed to have weak H‐hydrogen bonding between water and radical, including HS, in the exit channel. This observation supports the claim that such adducts in the exit channel are not very important for vibrational energy disposal in H‐atom transfer reactions …”

“…The rate constants for reaction (4) do not give linear Arrhenius plots, and experimental values for E a can be obtained only for certain temperature ranges. A curved Arrhenius plot of H 2 S was analyzed in the experimental study of Lafage et al, who recommended E a = 0.78 kcal mol −1 for temperatures above 294 K. 20 Recent theoretical works 21,22 confirm a non-Arrhenius behavior of the OH + H 2 S reaction with predicted ab initio barrier heights (difference between the energies of transition state and reactants) of 0.70 kcal mol −1 (CCSD(T) aug-cc-pV5Z level corrected for zero point vibrational energy 21 ) and 0.82 kcal mol −1 (MC-QCISD/3 level 22 ). Assignment of <E av > for reaction (4) was made taking E a = 0.75 kcal mol −1 .…”

“…The highest excitation observed in the H 2 S reactions was (v 1,3 ,v 2 ) = (3,0) (31.5 kcal mol −1 ), which suggests that <E av > is close to this value; this energy corresponds to the best calculated barrier of 0.7 kcal mol −1 . 21 Vibrational distributions obtained for H 2 O and HOD are presented in Tables 2 and 3, respectively. Simulation in the 3200-3900 cm −1 range gives P 1,3 (1-3) and P 3 (1-3) distributions designated in Tables 2 and 3 as P 1,3 b and P 3 b .…”