The importance of the HSO(2) system in atmospheric and combustion chemistry has motivated several works dedicated to the study of associated structures and chemical reactions. Nevertheless controversy still exists in connection with the reaction SH + O(2)→ H + SO(2) and also related to the role of the HSOO isomers in the potential energy surface (PES). Here we report high-level ab initio calculation for the electronic ground state of the HSO(2) system. Energetic, geometric, and frequency properties for the major stationary states of the PES are reported at the same level of calculations: CASPT2/aug-cc-pV(T+d)Z. This study introduces three new stationary points (two saddle points and one minimum). These structures allow the connection of the skewed HSOO(s) and the HSO(2) minima defining new reaction paths for SH + O(2) → H + SO(2) and SH + O(2) → OH + SO. In addition, the location of the HSOO isomers in the reaction pathways have been clarified.

The effect of reactants vibrational and rotational excitation on products (HO 2 + O and O 3 + H) formation is investigated for the title reaction by using the quasiclassical trajectory method and the realistic double manybody expansion (DMBE) potential energy surface for ground-state HO 3. It is shown that it can be a potential source of ozone in the upper atmosphere.

We report a theoretical study of the title four-atom atmospheric reaction for a range of translational energies 0.1 e E tr /kcal mol-1 e 40 and the range 13 e V′′ e 27 of vibrational quantum numbers of the oxygen molecule. All calculations have employed the quasiclassical trajectory method, and a realistic potential energy surface obtained by using the double many-body expansion (DMBE) method for ground-state HO 3 .

We discuss the dissociation of the OH radical in the title molecular collisions when both species are vibrationally excited. An analysis of the O 2 dissociation is also reported. All calculations employed the quasiclassical trajectory method and a realistic double many-body expansion (DMBE) potential energy surface for groundstate HO 3 . The results are compared with those referring to formation of HO 2 and O 3 under similar conditions. Possible implications on atmospheric models for ozone production are tentatively assessed.

The vibrational relaxation processes occurring during collisions of vibrationally excited O 2 and OH are investigated using the quasiclassical trajectory method and a realistic double many-body expansion (DMBE I) potential energy surface for ground-state HO 3 . A salient feature is the observation of multiquanta deactivation processes for such high internal energies. It is also shown that the vibrational relaxation of colliding molecules is far less important than the reactive processes leading to formation of "odd-oxygen" (and hence ozone) under stratospheric local thermodynamic disequilibrium conditions.