$S_{2} - S_{0}$ FLUOORESCENCE, MOLECULAR STRUCTRRE, AN INITIO CALCULATIONS, AND QUKANTUM BEAT SPECTROSCOPY OF SILYLIDENE $(H_{2}C=Si)$

Abstract

Strong $S_{2}-S_{0}$ fluorescence has been observed in LIF spectra of jet-cooled silylidene, $H_{2}C=Si$, produced by fragmentation of tetramethylsilane in a pulsed discharge jet. The experimental ground and excited state molecular structures have been obtained for the first time from rotational analyses of the $0^{0}_{0}$ bands of $H_{2}C = $Si and $D_{2}C=Si$. These bands exhibit pronounced rotational level intensity anomalies indicative of nonradiative decay processes. Quantum beats are observed in the fluorescence decay of almost every rotational level in $v^{\prime} = 0$ and in most of the higher vibrational levels. Fourier transforms of the beat patterns show line broadening and splitting at small magnetic fields of 10-70 Gauss. High quality ab initio studies have been done to locate the interacting electronic states and predict their vibrational frequencies and molecular structures.