Abstract
Following photodissociation of dimethyl disulfide (CH3SSCH3) in a supersonic jet with a KrF excimer laser at 248 nm, degenerate four-wave mixing (DFWM) spectra of the à 2A1 □ X 2E3/2 transition of CH3S (methylthio or thiomethoxy) in a spectral region 317□377 nm were recorded using a dye laser. In addition to extension to higher members of the known progressions 3v and 213v associated with C□S stretching (□3) and CH3 umbrella (□2) modes, new progressions involving the symmetric CH3 stretching (□1) mode of the à 2A1 state of CH3S were tentatively assigned. However, in this work of DFWM, detailed information on lifetimes of these predissociative states were difficult to obtain because of homogeneous broadening of rovibronic lines leading to overlapped band structures. We further applied two-color resonant four-wave mixing (TC-RFWM) with the hole-buring scheme to investigate these highly predissociative levels of CH3S. Because the spectral simplification afforded by the two-color method allows accurate determination of line positions and homogeneous line widths, we confirmed vibrational assignments of new progressions 113v and 11213v involving symmetric CH3 stretching mode (□1) and measured quantitatively their lifetimes. We also demonstrated predissociative levels of the B 3□- state of SO. Following photodissociation of SO2 in a supersonic jet with an ArF excimer at 193 nm, DFWM spectra of the B 3□-□ X 3□- transition of SO in a spectral region 220-263 nm were recorded using a frequency-doubled dye laser. The rotational analysis of (8,2), (8,1), and (8,0) bands yields spectral parameters of the B 3□- (v□ = 8) state that are significantly improved over those reported previously; parameters for centrifugal distortion (D□), spin-spin coupling (□□, and □D), and spin-rotation coupling (□□) were derived for the first time. We have also studied the spectra of CH2CO+ and CD2CO+ cations using nonresonant two-photon mass analyzed threshold ionization (MATI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. Fundamental wave numbers of several normal vibrational modes (six for CH2CO+ and seven for CD2CO+) of the 2B1 electronic ground state were determined; the □5, □6, □8, and □9 nontotally symmetric vibrational modes were observed for the first time. Rotational analysis of the ZEKE spectra has yielded the ionization potentials of the CH2CO and CD2CO isotopomers and the rotational constants for the ground state of the cations.