Carbamic acid and its dimer: A computational study

A recent work by Marks et al. on the formation of carbamic acid in NH 3‐CO 2 interstellar ices pointed out its stability in the gas phase and the concomitant production of its dimer. Prompted by these results and the lack of information on these species, we have performed an accurate structural, energetic and spectroscopic investigation of carbamic acid and its dimer. For the former, the structural and spectroscopic characterization employed composite schemes based on coupled cluster (CC) calculations that account for the extrapolation to the complete basis set limit and core correlation effects. A first important outcome is the definitive confirmation of the nonplanarity of carbamic acid, then followed by an accurate estimate of its rotational and vibrational spectroscopy parameters. As far as the carbamic acid dimer is concerned, the investigation started from the identification of its most stable forms. For them, structure and vibrational properties have been evaluated using density functional theory, while a composite scheme rooted in CC theory has been employed for the energetic characterization. Our results allowed us to provide a better interpretation of the feature observed in the recent experiment mentioned above. What is the smallest interstellar molecule containing both the carboxyl and amino groups? Carbamic acid and its dimers have been studied with accurate quantum‐chemical approaches as a first step toward their spectroscopic characterization, required to support any astronomical search.