CH3SH ULTRAVIOLET-ABSORPTION CROSS-SECTIONS IN THE REGION 192.5-309.5 NM AND PHOTODECOMPOSITION AT 222 AND 193 NM AND 296 K

The absolute ultraviolet absorption cross sections of methyl mercaptan (CH3SH) have been determined in the wavelength region 192.5-309.5 nm at 296 K. The uv absorbance, A, in a column of slowly flowing standard CH3SH/helium gas mixtures, was monitored in long Pyrex absorption cells of path length, l, at several different pressures at the ambient cell temperature using a diode-array spectrometer with an instrumental resolution ranging from 0.25 to 1.10 nm. The absorption cross sections, sigma=A/l[CH3SH], were calculated using the Beer-Lambert law from the known partial pressure of CH3SH in the gas mixture. The primary quantum yields of H atom produced in the 222 and 193 nm laser photolysis of CH3SH have been determined to be 0.95 +/- 0.10 and 0.49 +/- 0.08 relative to 248 nm CH3SH photolysis and 193 nm HBr photolysis, respectively, at 296 K. The H atoms were directly monitored in the photolysis by resonance fluorescence detection of (H(S))-S-2.