Far-Infrared Synchrotron Spectroscopy of a Potentially Important Interstellar Isotopologue of Vinyl Alcohol: CH2CHOD

New prebiotic molecules in the interstellar medium from the reaction between vinyl alcohol and CN radicals: unsupervised reaction mechanism discovery, accurate electronic structure calculations and kinetic simulations

Vinyl alcohol (VyA) and cyanide (CN) radicals are relatively abundant in the interstellar medium (ISM). VyA is the enolic tautomer of acetaldehyde and has two low-lying conformers, characterized by the syn or anti placement of hydroxyl hydrogen with respect to the double bond. In this paper, we present a gas-phase model of the barrierless reactions of both VyA's conformers with CN employing accurate quantum chemical computations in the framework of a master equation approach based on the transition state theory. Our results indicate that both VyA conformers feature a similar reactivity with CN, starting with a barrierless addition to the double bond and followed by different isomerization, dissociation, and/or hydrogen elimination steps. The rate constants computed for temperatures up to 600 K show that several reaction channels are open even under the harsh conditions of the ISM, with the favoured one providing the first feasible formation route of a prebiotic molecule not yet detected in the ISM, namely cyanoacetaldehyde. This finding suggests looking for cyanoacetaldehyde in regions where both VyA and CN have already been detected, like, e.g., Sagittarius B2N or G+0.693-0.027.

Characterization of the Coriolis Coupled Far-Infrared Bands of syn-Vinyl Alcohol

Rotational emission from vibrationally excited molecules are responsible for a large fraction of lines in the spectra of interstellar molecular clouds. Vinyl alcohol (VA) has two rotamers that differ in energy by 6.4 kJ/mol, both of which have been observed toward the molecular cloud, Sagittarius B2(N) [Turner and Apponi, Astrophys. J. 2001, 561, 207]. Previously, we reported an analysis of the far-infrared spectrum of the higher energy rotamer, anti-VA [Bunn et al. Astrophys. J. 2017, 847, 67], yielding rotational and higher order distortion constants in the first excited vibrational state, and here, we report an analysis of the far-infrared spectrum of the lower energy rotamer, syn-VA, whose spectrum is significantly more complicated on account of Coriolis interactions that result in perturbations to the rovibrational spectrum. We account for those perturbations with the inclusion of Coriolis coupling constants in the fit, which couples the first excited OH torsional (ν₁₅) and CCO bending (ν₁₁) states. Inclusion of them resulted in more physically meaningful rotational and centrifugal distortion constants, and allows for accurate pure rotational line predictions to be made up to high energies. These will be particularly useful in searches for vibrationally excited syn-VA toward warm regions of interstellar molecular clouds, where we predict that it may be significantly abundant.