Diminished cage effect in solid p-H2: Infrared absorption of CH3S observed from photolysis in situ of CH3SH, CH3SCH3, or CH3SSCH3 isolated in p-H2 matrices

We report the infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH3S ((XE3/2)-E-2), produced via photodissociation in situ of three precursors CH3SH, CH3SCH3, and CH3SSCH3 isolated in solid p-H-2. The common absorption features observed with similar intensity ratios in each experiment are assigned to CH3S. The wavenumbers of these features agree satisfactorily with those predicted with a spin-vibronic Hamiltonian accounting for the anharmonic effects and the Jahn-Teller effects to the quartic term [A. V. Marenich and J. E. Boggs, J. Chem. Theory Comput. 1, 1162 (2005)]. In addition to an absorption line at 724.2 cm(-1), corresponding to a transition of 3(1) previously determined to be 727 cm(-1) from fluorescence spectra of gaseous CH3S, we identified fundamental transitions 6(1)(a(1)) at 771.1, 6(1)(e) at 1056.6, 5(1)(a(1)) at 1400.0, 4(1)(a(1)) at 2898.4 cm(-1), and several combination and overtone transitions. In contrast, photolysis of CH3SSCH3 isolated in solid Ar produces mainly H2CS, CH3SH, and CS2, but no CH3S. These results demonstrate the feasibility of using photolysis in situ of precursors isolated in solid p-H-2 to produce free radicals by taking advantage of the diminished cage effect of the matrix. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502105]