Diminished cage effect in solid p-H₂: Infrared absorption of CH₃ S observed from photolysis in situ of CH₃ SH, CH ₃ SCH₃, or CH₃ SSCH₃ isolated in p-H₂ matrices

We report the infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH₃ S (X E2 3/2), produced via photodissociation in situ of three precursors CH₃ SH, CH₃ SCH₃, and CH₃ SSCH₃ isolated in solid p -H ₂. The common absorption features observed with similar intensity ratios in each experiment are assigned to CH₃ S. 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 31 previously determined to be 727 cm ^-1 from fluorescence spectra of gaseous CH₃ S, we identified fundamental transitions 61 (a₁) at 771.1, 61 (e) at 1056.6, 51 (a₁) at 1400.0, 41 (a₁) at 2898.4 cm ^-1, and several combination and overtone transitions. In contrast, photolysis of CH₃ SSCH₃ isolated in solid Ar produces mainly H₂ CS, CH₃ SH, and CS₂, but no CH ₃ S. These results demonstrate the feasibility of using photolysis in situ of precursors isolated in solid p -H₂ to produce free radicals by taking advantage of the diminished cage effect of the matrix.