José Luis Doménech

The rovibrational spectrum of the molecular ion H$_2$CCCH$^+$ was investigated in a 4~K cryogenic ion trap instrument employing the leak-out spectroscopy method. Transitions within the fundamental $ν_1$ (C-H stretch) and the combination band $ν_3$+$ν_5$ (C-C stretches) were detected, the search aided by high level quantum chemical calculations. The analysis of the rovibrational measurements enabled us to predict the rotational structure of the ground state. Using a rotational-vibrational double-resonance scheme, 14 pure rotational transitions were measured. This, in turn, led to the radio astronomical detection of H$_2$CCCH$^+$ in the interstellar medium, as recently reported (Silva et al., Astron. Astrophys. 676, L1, 2023).

We report rest frequencies for rotational transitions of the deuterated ammonium isotopologues NH3D+, NH2D2+ and NHD3+, measured in a cryogenic ion trap machine. For the symmetric tops NH3D+ and NHD3+ one and three transitions are detected, respectively, and five transitions are detected for the asymmetric top NH2D2+. While the lowest frequency transition of NH3D+ was already known in the laboratory and space, this work enables the future radio astronomical detection of the two other isotopologues.