Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl.

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 (2)A(") state, as well as the vertical energy from the equilibrium geometry of that excited state to the 2 (2)A(") state, to aid in the experimental assignment.