15min:

YUAN-PERN LEE, Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan; MOHAMMED BAHOU, Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan .

We report infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH₃S, isolated in solid p-H₂. CH₃S was produced by in situ UV photodissociation of three precursors: CH₃SH, CH₃SCH₃, and CH₃SSCH₃ isolated in solid p-H₂. New absorption features commonly observed with similar intensity ratios in experiments using these precursors are assigned as absorption of CH₃S. In addition to the previously assigned transitions of ₃ (a₁) at 727.1 cm^-1, fundamental transitions ₆ (a₁) at 771.1, ₆ (e) at 1056.6, ₅ (a₁) at 1400.0, and ₄ (a₁) at 2898.0 cm^-1 were observed. 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; the corresponding wavenumbers predicted from theory are ₆ (a₁) at 793, ₆ (e) at 1105, ₅ (a₁) at 1436, and ₄ (a₁) at 2938 cm^-1, with deviations of 1.4-4.6 % from experiments. Previous attempts of UV photolysis of CH₃SCH₃ and CH₃SSCH₃ isolated in an Ar matrix failed to produce CH₃S. These results serve as an excellent example that the diminished cage effect of solid p-H₂ makes production of free radicals via photolysis in situ feasible. If time permits, other examples will be discussed.