The first observation of transitions between bound electronic states of neutral helium hydride is reported. Excited molecules were produced by electron transfer to the corresponding molecular ions. Emission spectra in the visible were obtained. Five electronic bands could be identified for three isotopic mixtures. Molecular constants confirming recent calculations of potential curves were derived for the first time. Predissociation of the upper state occurs for ${}_{}{}^4{}_{}{}^{}\mathrm{HeH}$ in contrast to ${}_{}{}^3{}_{}{}^{}\mathrm{HeD}$. Also NeH spectra could be obtained by the same method.

• Received 9 October 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.2941