Evidence for a Be Isotope of Mass 8 and Fine Structure Measurements in the BeH Bands

Abstract

An intense spectrogram of the $\lambda 4991$ BeH band has been obtained in the third order of a 21-foot concave grating with a dispersion of 1.286A per mm. Every $P$ and $R$ line of the (0, 0) band in the strong interval $K^{\prime \prime }=6\mathrm{} \mathrm{to} 20$ is accompanied by a very weak line in the position calculated for ${\mathrm{Be}}^8$H, except where a strong line of another branch prevents measurement. The relative intensities of the ${\mathrm{Be}}^8$H and ${\mathrm{Be}}^9$H lines are about 1:2000. Discussion shows this to be a reliable indication of the presence of a small amount of a beryllium isotope of mass 8.