High Rydberg states of helium hydride

High-lying Rydberg states (11\ensuremath{\le}n\ensuremath{\le}34) of helium hydride have been observed. They were produced by laser excitation of a fast molecular beam and detected by field ionization. Ionization potentials, quantum defects, and the binding energy of ${\mathrm{HeH}}^{+}$ were determined. Pure rotational autoionization leads to break offs of the series. From missing lines it is concluded that B $^{2}\mathcal{'}$) state decays by predissociation.