Rotational state analysis of AlH⁺ by two-photon dissociation

We perform ab initio calculations relevant to predict the cross-section of an experimentally accessible (1+1^′) resonance-enhanced multiphoton dissociation (REMPD) pathway in AlH⁺. Experimenting on AlH⁺ ions held in a radiofrequency trap, we confirm dissociation via this channel with analysis performed using time-of-flight mass spectrometry, demonstrate the use of REMPD for rotational state analysis, and measure the rotational distribution of trapped AlH⁺ to be consistent with the expected thermal distribution. AlH⁺ is a particularly interesting species because its electronic level structure is compatible with proposals to perform rotational optical pumping, direct Doppler cooling, and single-molecule fluorescence detection. Potential applications of trapped AlH⁺ include searches for time-varying constants, quantum information processing, and ultracold chemistry studies.