Laser induced fluorescence of CH3S and CD3S radicals

摘要

Laserhyphen;induced fluorescence of the CH3S andCD3SAtilde;thinsp;2A1minus;Xtilde;thinsp;2Etransitions was studied. The 000bandhead of the2A1ndash;2E3/2transition lies at 26thinsp;531 cmminus;1(376.82 nm) for CH3S and 26thinsp;574 cmminus;1(376.20 nm) for CD3S. Prominent progressions of the Cndash;S stretching mode (ngr;3) both in the excitation and dispersed fluorescence spectra are characterized by a doublet structure corresponding to a spinhyphen;orbit splitting in the ground state. The band shapes of the transitions2A1ndash;2E1/2and2A1ndash;3E3/2were found to be quite different from each other, which was interpreted as the difference in the geometry of the spinhyphen;orbit sublevels. From the doublet spacings, a spinhyphen;orbit coupling constant (A) was obtained; minus;280plusmn;20 cmminus;1in CH3S and minus;260plusmn;20 cmminus;1in CD3S, in a good agreement with the previous results of laser electron photodetachment studies. The CH3umbrella mode vibration (ngr;2) is also active in the vibronic transition. Fundamental vibrational frequencies determined were 1316plusmn;4 (ngr;Prime;2), 740plusmn;4 (ngr;Prime;3), and 403plusmn;1 cmminus;1(ngr;prime;3) for CH3S, and 837plusmn;1 (ngr;2), 667plusmn;1 (ngr;Prime;3) and 395plusmn;1 cmminus;1(ngr;3) for CD3S. Fluorescence lifetimes of single vibronic levels were measured to give 0.31 mgr;s for the 000band of CH3S. Predissociation occurs atvprime;3=2 and 3 for CH3S and CD3S, respectively.