Unimolecular pathways for the isomerization and/or dissociation of HSOO, HOSO, HSO 2 , and HOOS to H + SO 2 and OH + SO have been investigated computationally, as well as HSO formation via an HSOO intermediate. The atmospheric lifetime of HSO 2 is discussed. Some pathways have no barrier, including OH + SO f HOSO and H + SOO f HSOO and SOOH, while structures and vibrational frequencies of transition states for HOSO f H + SO 2 , HOOS f OH + SO, HOSO f HSO 2 , HSOO f HS + O 2 , and HSO 2 f H + SO 2 have been characterized at the MP2)FULL/6-31G(d) level. Some geometries were further refined at the QCISD/6-311G(d,p) level. Gaussian-2 theory was employed to calculate approximate QCISD(T)/6-311+G-(3df,2p) energy barriers, and the kinetics were analyzed by RRKM theory. Rate constant expressions at the high and low-pressure limits and thermochemical properties for transient intermediates are tabulated, and the results are discussed in the context of atmospheric and combustion chemistry. A revised theoretical H-OSO bond strength is compatible with the flame data for SO 2 -catalyzed recombination of H atoms.

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Geometries and vibrational frequencies of five isomers of H2S02 have been derived at the HF/3-21G(*) and MP2/3-21G(*) levels of theory, and energies were obtained using MP4/6-31GS//MP2/3-21G(*) theory. In order of decreasing stability the isomers are S(OH)2, HSOzH (sulfinic acid, two conformers), sulfone, HSOOH, and H2SO0. Pathways leading to HS02H formation were analyzed to determine why the more stable S(OH), was not seen in matrix-isolation experiments. The barrier to isomerization between the two isomers was estimated to be 190 kJ mol-' relative to HS02H, and the stability of HS02H with respect to dissociation was also considered.

Structures and vibrational frequencies for minima and 11 transition states on the O(3P)+H2S potential energy surface have been characterized at the MP2=FULL/6-31G(d) level. GAUSSIAN-2 theory was employed to calculate ΔHf,298 for HSO and HOS of −19.9 and −5.5 kJ mol−1, respectively. The kinetics of HSO=HOS isomerization are analyzed by Rice–Ramsperger–Kassel–Marcus theory. Transition state theory analysis for O+H2S suggests OH+HS is the dominant product channel, with a rate constant given by 1.24×10−16 (T/K)1.746 exp(−1457 K/T) cm3 molecule−1 s−1. Kinetic isotope effects and the branching ratio for H+HSO production are also analyzed. The other possible products H2+SO and H2O+S do not appear to be formed in single elementary steps, but low-barrier pathways to these species via secondary reactions are identified. No bound adducts of O+H2S were found, but results for weakly bound triplet HOSH are presented. The likely kinetics for the reactions OH+SH→S(3P)+H2O, OH+SH→cis and trans 3HOSH, cis 3HOSH→HOS+H, and HSO and HOS+H→H2+3SO are discussed.

The recombination of atomic potassium, K(42S), with SO2 has been investigated at about 863 K, in a bath of Ar at pressures from 20 to 690 mbar. K was generated by flash photolysis of KI vapor and monitored by time-resolved resonance absorption of a D-line at 766 nm under pseudo-first-order conditions. The measured pseudo-second-order rate constants lie in the low-pressure and falloff regions and were fitted with an empirical RRKM expression to yield ko = 5.9 X cm6 s-l and k, = 6.2 X 1O-l0 cm3 s-l. Error limits are discussed in the text. The KSOz adduct was characterized by ab initio methods. An RRKM analysis of ko, together with a lower limit to the equilibrium constant, yielded a K S 0 2 bond strength of 190 f 10 kJ mol-'. k, was shown to be consistent with a simple harpoon model for electron transfer.