Knowledge Bank

“The flash photolysis of chlorosilane and bromosilane has yielded extensive band systems which have been aligned to HSiCl and HSiBr. In each radical there is a progression of absorption bands extending from 4800 to shorter wavelengths, and in addition, a progression of fluorescent bands extending to longer wavelengths. Each band has a very wide K structure, and each sub-band has a very narrow J structure which is fully resolved only under the highest resolution. The most striking aspect of the new spectra is the observation of transitions with $\Delta K=0,\pm 2$, in addition to those with $\Delta K=\pm 1$. Only the latter should occur since it can be shown than the transition moment is perpendicular to the plane of the molecule, and therefore, the bands are pure perpendicular bands Another peculiarity observed in these spectra is the occurrence of the transition $\Delta J=O$ in the sub-band $K\prime =O\leftarrow K″=O$. These peculiarities can he accounted for if it is assumed that the electronic transition is a triplet.-singlet transition However, no triplet splitting has yet been resolved. Rotational constants for HSiCl, DSiCl, and HSiBr have been determined in both upper and lower states.”