Photoabsorption and photoionization of HeH⁺

The photoabsorption spectrum of the HeH⁺ molecular ion is investigated. The theoretical study includes transitions to electronically excited states and to the ionization continuum. The influence of autoionizing resonances is discussed. In the absorption spectrum, vibrational motion is considered within the Born-Oppenheimer approximation, whereas the reflection approximation is applied for the photoionization spectrum. The importance of the photoabsorption spectrum for the ongoing tritium neutrino-mass experiments is discussed. In order to assess the accuracy of the numerical approach, the doubly excited states of HeH⁺ (position and width) and the photoionization spectrum of H₂ are compared to literature data.