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

• Published in: The Journal of chemical physics 2009-07, Vol.131 (4)
• Main Authors: Alligood, Bridget W., FitzPatrick, Benjamin L., Glassman, Emily Jane, Butler, Laurie J., Lau, Kai-Chung
• Format: Article
• Language: English
• Subjects: BEAMS; CHALCOGENIDES; CHARGED PARTICLES; CHEMICAL REACTIONS; DECOMPOSITION; DETECTION; DISSOCIATION; DISTRIBUTION; ELECTRON BEAMS; ENERGY; ENERGY LEVELS; ENERGY-LEVEL TRANSITIONS; EQUILIBRIUM; EXCITATION; EXCITED STATES; FISSION; GROUND STATES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IONS; KINETIC ENERGY; LEPTON BEAMS; MOLECULAR BEAMS; NUCLEAR REACTIONS; ORGANIC COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; PARTICLE BEAMS; PHOTOCHEMICAL REACTIONS; PHOTOLYSIS; RADICALS; RECOILS; SULFUR COMPOUNDS; SULFUR DIOXIDE; SULFUR OXIDES; VELOCITY; VIBRATIONAL STATES
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3159555

The dissociation dynamics of methylsulfonyl radicals generated from the photodissociation of CH{sub 3}SO{sub 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{sub 3}SO{sub 2} radicals, S-Cl fission to produce Cl atoms and electronically excited CH{sub 3}SO{sub 2} radicals, and S-CH{sub 3} fission. Some of the vibrationally excited CH{sub 3}SO{sub 2} radicals undergo subsequent dissociation to CH{sub 3}+SO{sub 2}, as do all of the electronically excited radicals. The velocities of the SO{sub 2} products show that the vibrationally excited ground state CH{sub 3}SO{sub 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{sub 2} products. The electronically excited CH{sub 3}SO{sub 2} radicals also dissociate to CH{sub 3}+SO{sub 2}, but with a larger average release to relative kinetic energy. Interestingly, when using 200 eV electron bombardment detection, the ground electronic state CH{sub 3}SO{sub 2} radicals having too little internal energy to dissociate are not observed at the parent CH{sub 3}SO{sub 2}{sup +} ion, but only at the CH{sub 3}{sup +} 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{sub 3}SO{sub 2} to CH{sub 3}+SO{sub 2}. We present CCSD(T) calculations of the adiabatic excitation energy to the lowest excited state of CH{sub 3}SO{sub 2} radicals, the 1 {sup 2}A{sup ''} state, as well as the vertical energy from the equilibrium geometry of that excited state to the 2 {sup 2}A{sup ''} state, to aid in the experimental assignment.