Journal of Chemical Physics, Vol.101, No.7, 5596-5603, 1994
Nonresonant 2-Photon Pulsed-Field Ionization of Ch3S Formed in Photodissociation of Ch3Sh and Ch3Ssch3
Threshold photoelectron (PE) spectra for CH3S formed in the photodissociation of CH3SH and CH3SSCH3 in the photon energy range of 36 850-38 150 cm(-1) have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. Both spin-orbit states CH3S(($) over tilde X (2)E(3/2)) and CH3S((2)E(1/2)) are observed from CH3SH and CH3SSCH3 in this photodissociation energy range. However, negligible intensities of vibrationally excited CH3S radicals are produced from CH3SH. In the case of CH3S from CH3SSCH3, the population ratio CH3S(upsilon(3)=1)/CH3S(upsilon(3)=0) is estimated to be approximate to 0.18. The simulation of the N2P-PFI-PE spectra reveals that the rotational temperature for CH3S(($) over tilde X (2)E(3/2,1/2)) formed by photodissociation of CH3SH is approximate to 200-250 K and the branching ratio CH3S((2)E(1/2))/CH3S(($) over tilde X (2)E(3/2)) is 0.5+/-0.1. For CH3S(($) over tilde X (2)E(3/2,1/2)) produced from CH3SSCH3, the rotational temperature for CH3S(($) over tilde X (2)E(3/2,1/2)) is approximate to 800-900 K and the branching ratio CH3S((2)E(1/2))/CH3S(($) over tilde X (2)E(3/2)) is 1.1+/-0.2. This experiment demonstrates that the PFI-PE spectroscopic method can be a sensitive probe for nascent rovibronic state distributions of photoproducts. Furthermore, the simulation also shows that the photoionization dynamics of CH,S may involve rotational angular momentum changes up to +/-4. The ionization energy and C-S stretching frequency for CH3S+(($) over tilde X (3)A(2)) are determined to be 74 726+/-8 cm(-1) (9.2649+/-0.0010 eV) and 733+/-5 cm(-1), respectively. The spin-orbit splitting for CH3S(($) over tilde X (2)E(3/2,1/2)) is 257+/-5 cm(-1), in agreement with the literature values.
Keywords:ENERGY PHOTOELECTRON-SPECTRUM;LASER-INDUCED FLUORESCENCE;193 NM PHOTODISSOCIATION;ELECTRONIC GROUND-STATE;ULTRAVIOLET PHOTODISSOCIATION;ROTATIONAL ANALYSIS;METHYL MERCAPTAN;NITRIC-OXIDE;RESOLUTION;PHOTOIONIZATION