Toward the laboratory identification of the not-so-simple NS2neutral and anion isomers

Anharmonic fundamental vibrational frequencies and spectroscopic constants of the potential HSO2 radical astromolecule

The recent report that HSO₂ is likely kinetically favored over the HOSO thermodynamic product in hydrogen addition to sulfur dioxide in simulated Venusian atmospheric conditions has led to the need for reference rotational, vibrational, and rovibrational spectral data for this molecule. While matrix-isolation spectroscopy has been able to produce vibrational frequencies for some of the vibrational modes, the full infrared to microwave spectrum of 1 ²A' HSO₂ is yet to be generated. High-level quantum chemical computations show in this work that the >2.5 D dipole moment of this radical makes it a notable target for possible radioastronomical observation. Additionally, the high intensity antisymmetric S-O stretch is computed here to be 1298.3 cm^-1, a 13.9 cm^-1 blueshift up from H₂ matrix analysis. In any case, the full set of rotational and spectroscopic constants and anharmonic fundamental vibrational frequencies is provided in this work in order to help characterize HSO₂ and probe its kinetic favorability.

Highly Accurate Quartic Force Field and Rovibrational Spectroscopic Constants for the Azirinyl Cation (c-C2NH2+) and Its Isomers

The azirinyl cation is an aromatic cyclic molecule that is isoelectronic with cyclopropenylidene, c-C₃H₂, and c-C₃H₃⁺. Cyclopropenylidene has been shown to be ubiquitous, existing in many different astrophysical environments. Given the similar chemistry between C and N, and the relative abundances between C and N in astrophysical environments, it is expected that there should be aromatic ringed molecules that incorporate N in the ring, but as yet, no such molecule has been identified. To address this issue, the present study uses high levels of electronic structure theory to compute a highly accurate quartic force field (QFF) for the azirinyl cation and its two lowest lying isomers, the cyanomethyl and isocyanomethyl cations. The theoretical approach uses the singles and doubles coupled-cluster method that includes a perturbative correction for connected triple excitations, CCSD(T), together with extrapolation to the one-particle basis set limit and corrections for scalar relativity and core-correlation. The QFF is then used in a second-order vibrational perturbation theory analysis (VPT2) to compute the fundamental vibrational frequencies and rovibrational spectroscopic constants for all three C₂NH₂⁺ isomers. The reliability of the VPT2 vibrational frequencies is tested by comparison to vibrational configuration interaction (VCI) calculations, and excellent agreement is found between the two approaches. Fundamental vibrational frequencies and rovibrational spectroscopic constants for all singly substituted ¹³C, ¹⁵N, and D isotopologues are also reported. It is expected that the highly accurate spectroscopic data reported herein will be useful in the identification of these cations in high-resolution experimental or astronomical observations.