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 radicals (OH), which plays an important role in producing sulfuric acid and sulfates in the Earth's atmosphere, was computed by 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 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 the temperature range T = 10–2500 K and a wide pressure range, is found to be effectively independent of pressure for T = 200–2500 K, in which range k₁(T) can be represented by . 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: , based on the ab initio results of this work and the available experimental determinations.