Knowledge Bank

Strong $S2-S0$ fluorescence has been observed in LIF spectra of jet-cooled silylidene, $H2C=Si$, 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 $000$ bands of $H_{2}C = $Si and $D2C=Si$. 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.