Highly predissociative levels of CH_3S(A~2A_1)detected with degenerate four-wave mixing

摘要

Following photodissociation of dimethyl disulfide (CH_3SSCH_3) in a supersonic jet with a KrF excimer laser at 248 nm,degenerate four-wave mixing spectra of the A~2a_1<-X~2E_3/2 transition of CH_3S in a spectral region 317-377 nm are recorded using a dye laser.Observed features extend to 5020 cm~-1 above the origin,much greater than 1490 cm~-1 for fluorescence spectra adn 2979 cm~-1 for fluorescence depletion spectra.In addition to extension to higher members of the known progressions 3~v AND 2~13~v associated with C-S stretching (v_3)adn CH_3 mubrella (v~2)modes,three new progressions 1~13~v,3~v4~1,and 2~13~v4~1 (or 1~12~13~v)involving the symmetric CH_3 stretching (v_1)and asymmetric CH_3 stretching (v_1)and asymmetric CH_3(v_4)stretching modes of the A~2A_1 state of CH_3S are tentatively assigned,yielding values of v_1=2966 cm~-1 and v_4=3006 cm~-1 that are consistent with theoretical predictions.Vibrational spectral parameters for v_1,v_2,v_4 and v_4 modes of the A~2A_1 state of CH_3S are derived.