Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH 3 SO 2 Cl

• Published in: The Journal of chemical physics 2009-07, Vol.131 (4), p.044305-044305-14
• Main Authors: Alligood, Bridget W., FitzPatrick, Benjamin L., Glassman, Emily Jane, Butler, Laurie J., Lau, Kai-Chung
• Format: Article
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3159555

The dissociation dynamics of methylsulfonyl radicals generated from the photodissociation of CH 3 SO 2 Cl at 193 nm is investigated by measuring product velocities in a crossed laser-molecular beam scattering apparatus. The data evidence three primary photodissociation channels of the precursor: S-Cl fission to produce Cl atoms and ground electronic state CH 3 SO 2 radicals, S-Cl fission to produce Cl atoms and electronically excited CH 3 SO 2 radicals, and S - CH 3 fission. Some of the vibrationally excited CH 3 SO 2 radicals undergo subsequent dissociation to CH 3 + SO 2 , as do all of the electronically excited radicals. The velocities of the SO 2 products show that the vibrationally excited ground state CH 3 SO 2 radicals dissociate via a loose transition state having a small exit barrier beyond the endoergicity. Hence, a statistical recoil kinetic energy distribution should and does fit the distribution of velocities imparted to these SO 2 products. The electronically excited CH 3 SO 2 radicals also dissociate to CH 3 + SO 2 , but with a larger average release to relative kinetic energy. Interestingly, when using 200 eV electron bombardment detection, the ground electronic state CH 3 SO 2 radicals having too little internal energy to dissociate are not observed at the parent CH 3 SO 2 + ion, but only at the CH 3 + daughter ion. They are distinguished by virtue of the velocity imparted in the original photolytic step; the detected velocities of the stable radicals are consistent with the calculated barrier of 14.6 kcal/mol for the dissociation of CH 3 SO 2 to CH 3 + SO 2 . We present CCSD(T) calculations of the adiabatic excitation energy to the lowest excited state of CH 3 SO 2 radicals, the 1 A 2 ″ state, as well as the vertical energy from the equilibrium geometry of that excited state to the 2 A 2 ″ state, to aid in the experimental assignment.