Toward the laboratory identification of the not-so-simple NS2 neutral and anion isomers

Abstract

The NS radical is a simple arrangement of atoms with a complex electronic structure. This molecule was first reported by Hassanzadeh and Andrew's group [J. Am. Chem. Soc. 114, 83 (1992)] through Ar matrix isolation experiments. In the quarter century since this seminal work was published, almost nothing has been reported about nitrogen disulfide even though NS is isovalent with the common NO. The present study aims to shed new insight into possible challenges with the characterization of this radical. No less than three potential energy surfaces all intersect in the C region of the SNS radical isomer. A type-C Renner-Teller molecule is present for the linear Π state where the potential energy surface is fully contained within the 2.05 kcal/mol lower energy X̃ A state. A C, 1 B state is present in this same region, but a double excitation is required to access this state from the X̃ A state of SNS. Additionally, a 1 A NSS isomer is also present but with notable differences in the geometry from the global minimum. Consequently, the rovibronic spectrum of these NS isomers is quite complicated. While the present theory and previous Ar matrix experiments agree well on isotopic shifts, they differ notably for the absolute fundamental vibrational frequency transitions. These differences are likely a combination of matrix shifts and issues associated with the neglect of non-adiabatic coupling in the computations. In either case, it is clear that high-resolution gas phase experimental observations will be complicated to sort. The present computations should aid in their analysis.

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

“…The isolation of the three C 2 NH 2 + isomers on the global PES allows us to study their structure, vibrational spectra, and rovibrational spectroscopic constants via the well-established procedure of second-order vibrational perturbation theory (VPT2) using high-quality ab initio quartic force fields (QFF). The detailed procedure used here is described in refs − with some recent examples in refs , , , and . A recent high-resolution experiment has confirmed the reliability and accuracy of our predictions for C 3 H 3 + .…”

Quantum Chemical Rovibrational Analysis of the HOSO Radical

“…The least-squares fitting is tight (on the order of 1 × 10 −15 a.u. 2 ) and produces the equilibrium geometry. A refitting provides the force constants resulting from the refit zero gradients.…”

“…However, the namesake of this festschrift produced many experimental studies on small molecules containing sulfur, and recent quantum chemical computations are filling the remaining voids. The highly electronically complicated NS 2 radical , is a prime example of how experiments on sulfurous molecules from a few decades ago are only now coming under quantum chemical scrutiny beyond initial, contemporary studies …”

Hydrogen Sulfide as a Scavenger of Sulfur Atomic Cation

“…Additionally, the anharmonic vibrational frequencies are computed for each spin state of H 2 SS + in order to provide accurate, anharmonic zero-point vibrational energy corrections and insights gained from the vibrational structure of H 2 SS + . A fourth-order Taylor series expansion of the potential within the internuclear Hamiltonian (a quartic force field or QFF) is constructed in a standard fashion − but only utilizing CCSD­(T)-F12/aug-cc-pVTZ instead of a composite QFF approach, as is typical, including work on the S 2 H radical that ultimately led to its interstellar detection . From the reference geometries, 665 total points are computed on the basis of displacements of the below symmetry-internal coordinates: …”