High-Accuracy Theoretical Rate Coefficients for the Reaction of H2S with OH

Abstract

The rate coefficient for the reaction of hydrogen sulfide (H₂S) with hydroxyl radical (OH), which plays an important role in producing sulfuric acid and sulfates in the Earth’s atmosphere, was computed combining the high-accuracy coupled-cluster HEAT-345Q(P) method for energetics, W. H. Miller’s semi-classical transition state theory (SCTST) and two-dimensional E,J-resolved master equation analysis (2DME) for the kinetics. The title reaction proceeds by H-abstraction through a well-skipping mechanism directly yielding products, H₂O + SH. Tunneling effects are found to be important at the extremely low temperatures of the Interstellar Medium, but insignificant above 300 K. The rate coefficient k1(T,P) calculated over a temperature range T = 10 – 2500 and a wide pressure range, is found effectivelyindependent of pressure for T = 200 – 2500 K, in which range k1(T) can be represented by k1(T)=1.44×10^-16×T^1.674×exp⁡(+257T) cm³ s^-1. The results agree within 30% with the experimental data available in the T range of 230 to 550 K. For the range of 200 – 500 K of atmospheric interest, we recommend the rate coefficient expression k1(T) =9.28×10^-16×T^1.325×exp⁡(+286T) cm³ s^-1, based on the ab initio results of this work and the available experimental determinations.