Interstellar spectroscopic detection of HC(S)NC and DC(S)NC

Abstract

The detection of HC(S)CN in TMC-1 suggests that HC(S)NC may also exist. To aid in its possible detection, HC(S)NC and its deuterated isotopologue DC(S)NC were investigated via high-level ab initio methods, specifically CCSD(T) and CCSD(T)-F12. By utilizing multidimensional potential energy surfaces derived from explicitly correlated coupled-cluster calculations, we analyzed their geometrical parameters, vibrational frequencies, rotational constants, and a comprehensive set of spectroscopic constants generated via the vibrational second-order perturbation theory, vibrational self-consistent field, and vibrational configuration interaction theory(VCI) approaches. HC(S)NC is thermodynamically stable relative to the HCS + NC dissociation limit, with a predicted bond dissociation energy of 4.1 eV. The calculated vibrational frequencies are characterized by two bright modes that correspond to CN stretching. Finally, HC(S)NC shows a significant dipole moment, predicted to be 1.9 D, making its detection via rotational spectroscopy plausible.