H-atom product channel and mode specificity in the near-UV photodissociation of thiomethoxy radical via the Ã2A1 state

Abstract

Photodissociation of jet-cooled thiomethoxy radical (CH 3S) via the A ˜ 2 A 1 ← X ˜ 2 E 3 / 2 transition is studied in the region of 344–362 nm. The H-atom product channel is directly observed by H-atom photofragment yield spectrum and photofragment translational spectroscopy. Two vibronic levels of A ˜ 2 A 1 , 2 13 1 and 2 13 2, dissociate to H + H 2CS, while the others in the vicinity (2 13 3 and 3 n , n = 3–6) dissociate to CH 3 + S( 3P J) (based on a previous study by Neumark and co-workers). The H + H 2CS product translational energy release is not repulsive and peaks at ∼9 kcal/mol; the H-atom angular distribution is isotropic. The dissociation mechanism is consistent with internal conversion of the excited A ˜ 2 A 1 to the ground state X ˜ 2 E followed by unimolecular dissociation of X ˜ 2 E .