DETECTION OF SILYLENE AND GERMYLENE RADICALS BY LASER-INDUCED FLUORESCENCE

Silylene and germylene radicals are generated in the supersonic free j et by ArF laser photolysis of phenylsilane and phenylgermane, respecti vely. Laser-induced fluorescence (LIF) excitation and dispersed spectr a of the A1B1-X1A1 transition were measured for these radicals, and vi brational and rotational analyses were carried out. Heterogeneous pred issociation to Si(3P) + H-2 is proposed from the anomalous rotational structure in the excitation spectra; the rotational lines of the p(1) subbranch (K(a)' = 0 <-- K(a)'' = 1) have a stronger intensity than th ose of the r(0) subbranch (K(a)' = 1 <-- K(a)'' = 0), though the latte r is expected to be stronger due to the low temperature rotational dis tribution in the jet. The time-resolved excitation spectra demonstrate a shorter lifetime of K(a)' = 1 rovibronic levels than that of K(a)' = 0 levels in the AB-1(1) state. The mechanism of the heterogeneous pr edissociation is discussed. The onset of the second predissociation ch annel yielding Si(1D) + H-2 is manifested at the (0, 7, 0) vibronic le vel of the AB-1(1) state as a sharp decrease in the observed fluoresce nce lifetime for this level relative to that predicted for a pure radi ative lifetime. The LIF spectra of the AB-1(1)-X1A1 transition of germ ylene were measured in the wavelength region of 514-614 nm for the fir st time. Vibrational analysis of the bending mode was carried out. The LIF excitation spectrum suggests the predissociation mechanism simila r to that of SiH2 is operative.