Emission and Absorption Spectra of BaF

Comparison of the emission and absorption spectra of BaF under high dispersion shows that all of the known band systems involve the normal state of the molecule. The following electronic terms and vibration frequencies are established: $A$, $0({\omega }_e=469.1)$; $B$, 11,646.3 and 12,280.4 (437.7); $C$, 14,064.5 (424.6); $D$, 19,998.2 and 20,197.2 (455.8); $E$, 24,152.3 and 26,222.3 (506.6). Terms $A$ and $B$ have already been recognized as ${}_{}{}^2{}_{}{}^{}\Sigma$ and ${}_{}{}^2{}_{}{}^{}\Pi$ states, while $C$ is known to be an excited ${}_{}{}^2{}_{}{}^{}\Sigma$ state. The term $D$ is shown in the present work to constitute an electronic doublet, and another doublet state, $E$, is identified by the discovery of a new band system in the ultraviolet. Some changes are made in previous assignments of vibrational quantum numbers in the $B\rightleftarrows A$ system. Electronic terms and vibration frequencies for the analogous molecules LaO, SrF, YO, CaF, and ScO are tabulated, some of these having been re-evaluated from the original data on the basis of the new interpretation.