Detection of silylene and germylene radicals by laser-induced fluorescence

Abstract

Silylene and germylene radicals are generated in the supersonic free jet by ArF laser photolysis of phenylsilane and phenylgermane, respectively. Laser-induced fluorescence (LIF) excitation and dispersed spectra of the à 1B 1-à 1A 1 transition were measured for these radicals, and vibrational and rotational analyses were carried out. Heterogeneous predissociation 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 = O → K a = 1) have a stronger intensity than those of the r(O) subbranch ( K' a = 1 → K a = O), though the latter is expeced to be stronger due to the low temperature rotational distribution in the jet. The time-resolved excitation spectra demonstrate a shorter lifetime of K' a = 1 rovibronic levels than that of K' a = O levels in the à 1B 1 state. The mechanism of the heterogeneous predissociation is discussed. The onset of the second predissociation channel yielding Si( 1D) + H 2 is manifested at the (0,7,0) vibronic level of the à 1B 1 state as a sharp decrease in the observed fluorescence lifetime for this level relative to that predicted for a pure radiative lifetime. The LIF spectra of the à 1B 1-X̃ 1A 1 transition of germylene were measured in the wavelength region of 514–614 nm for the first time. Vibrational analysis of the bending mode was carried out. The LIF excitation spectrum suggests the predissociation mechanism similar to that of SiH 2 is operative.