The Ultraviolet Bands of Beryllium Chloride

A band system in the near ultraviolet region (3468-3700A) is obtained by using a beryllium arc in an atmosphere of chlorine. Four heads are found for each band, the ${}_{}{}^S{}_{}{}^{}R_{21}^{}{}_{}{}^{}$ heads being about one-third as intense as the other heads. The system is due to a ${}_{}{}^2{}_{}{}^{}\Pi -{}_{}{}^2{}_{}{}^{}\Sigma$ transition with the ${}_{}{}^2{}_{}{}^{}\Pi$ state an intermediate one between case a and case b. A complete rotational analysis is impossible but from the spacing of the lines in certain branches, $B^{\prime }≌0.8$ and $\frac{A}{B}≌31$. The isotope effect for chlorine is observed in -1 and +1 sequences and the ${}_{}{}^S{}_{}{}^{}R_{21}^{}{}_{}{}^{}$ head of the (0,0) band. From the heats of dissociation, it appears that the electronic excitation is due to the ${}_{}{}^1{}_{}{}^{}D\to {}_{}{}^1{}_{}{}^{}P$ transition in the beryllium atom.