Rotational spectroscopy of imidazole: Accurate spectroscopic information for three vibrationally excited states and the heavy-atom isotopologues up to 295 GHz

• Published in: Journal of molecular spectroscopy 2021-04, Vol.378, p.111452, Article 111452
• Main Authors: Arenas, Benjamin E., Batra, Gayatri, Steber, Amanda L., Bizzocchi, Luca, Pietropolli Charmet, Andrea, Giuliano, Barbara M., Caselli, Paola, Harris, Brent J., Pate, Brooks H., Guillemin, Jean-Claude, Schnell, Melanie
• Format: Article
• Language: English
• Subjects: Astrochemistry; Chemical Sciences; Imidazole; Isotopologues; Molecular structure; Rotational spectroscopy; Vibrationally excited states
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2021.111452

[Display omitted] •Imidazole was studied between 2–295 GHz; hydantoin was studied between 18–26 GHz.•Three vibrationally excited states of imidazole were observed and assigned.•Isotopologue analysis allowed gas-phase structure determination for both molecules.•Imidazole, hydantoin, and imidazolidine structures and vibrations are compared.•Precise rotational constants and line lists are delivered for all assigned species. We report our analysis of the pure rotational spectra of low-lying vibrationally excited states and heavy-atom rare isotopologues of imidazole. To facilitate searches for imidazole in the interstellar medium, we previously described the analysis of the rotational spectrum of the imidazole main isotopologue across the 2–295 GHz range, and we extend this analysis here. Structure optimisation and anharmonic frequency calculations were performed to aid the spectral analysis. Three vibrationally excited states of imidazole were assigned in our room-temperature spectra, with energies up to approximately 670 cm−1 above the vibronic ground state. The vibrational states could act as temperature probes in warmer star-forming regions. The 13C and 15N heavy-atom isotopologues were assigned, which allowed for the structure of imidazole in the gas phase to be determined. Structural comparisons are drawn between the related heterocyclic molecules hydantoin and imidazolidine. An experimental gas-phase structure of the former is also determined in this work. The potential detection of the isotopologues could help deduce formation pathways towards imidazole and other nitrogen-containing cyclic compounds in interstellar space.