Ultraviolet Spectra of BeH and BeH+

A BeH band system analogous to the $B{}_{}{}^2{}_{}{}^{}\Pi \to X{}_{}{}^2{}_{}{}^{}\Sigma$ MgH system is reported. Observed bands are the (0,0) at 1960A, (1,0) at 1882A and (1,1) at 1956A. Each consists of a single $Q$ branch (negligible spin doubling), $P$ and $R$ branch transitions being eliminated by predissociation from the ${}_{}{}^2{}_{}{}^{}\Pi$ state into a neighboring unstable ${}_{}{}^2{}_{}{}^{}\Sigma$ state. For the ${}_{}{}^2{}_{}{}^{}\Pi$ state $B_0=10.65\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and ${\omega }_e-2\mathrm{}{x}_e{\omega }_e=2133.4\mathrm{}$. The complex BeH spectrum from 3100A to 3600A consists only of an extension of the known ${}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}\mathrm{rightarrow}{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ Be${\mathrm{H}}^{+}$ system. Analyses of the principal Be${\mathrm{H}}^{+}$ bands in this region yield revised values for the band constants.