Silylene radicals, SiH, and SiD, , are generated in a supersonic free jet by ArF laser ( 193 nm) photolysis of phenylsilane and phenylsilane-a-d, , respectively. LIF excitation and dispersed fluorescence spectra are measured for the vZ vibronic bands of the 2 'B, -2 'A, transition. The heterogeneous predissociation to Si (3P) + H, is proposed from the anomalous rotational structure in the excitation spectra; the rotational lines of the r( 1) subbranch (K : = 0 +K I= 1) have stronger intensity

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... an those of the r( 0) subbranch (K i = 1 +K 1 = 0), though the latter is expected to be stronger due to the low temperature Boltzmann distribution in the jet. The time-resolved excitation spectra demonstrate shorter lifetime of K :, = 1 rovibronic levels in the 1 'B, state. The heterogeneous predissociation is interpreted with the second order perturbation: 2 'B, -(u-type Coriolis) +x 'A, -(spinorbit) +ii 3B' + Si( 3P) + H, . It is demonstrated experimentally that there is a potential barrier associated with the dissociation path of 5 3B' -+ Si( 3P) + H, , the height of which is estimated to be 1540-2160 cm-' from the bottom of the 2 'B' state. The electronic transition moment of the 1 'B, -2 'A' transition is estimated to be 1~~ I2 = 0.26e'az from the Einstein equation for spontaneous emission using measured fluorescence lifetimes for single rovibronic levels with K: = 0 and calculated Franck-Condon factors. The onset of a second predissociation channel, 2 'B' +Si( 'D) + H" at the (0,7,0) vibronic level of SiH, 2 'B' is manifested as a sharp decrease in the observed fluorescence lifetime for the v; = 7, J' = 0 level relative to that predicted for a pure radiative lifetime. 44