Fundamental vibrational frequencies of pnictogen (Pn) containing linear triatomic anions: OCPn^- and SCPn^- where Pn = N, P, As and Sb

Abstract

The fundamental vibrational frequencies of the isolated OCAs${}^{-}$ and SCAs${}^{-}$ ions, as well as their heavier antimony analogues, are reported for the first time. A thorough analysis of basis set convergence of the bond lengths and harmonic vibrational frequencies, as well as the examination of anharmonic corrections, is conducted using the MP2 and CCSD(T) ab initio methods with robust basis sets for the OC$P{n}^{-}$ and SC$P{n}^{-}$ anions moving down the pnictogen series from Pn = N to Sb. Second-order vibrational perturbation theory (VPT2) and vibrational configuration interaction (VCI) theory are used to compute the fundamental vibrational frequencies of each triatomic anion approaching the MP2 and CCSD(T) complete basis set (CBS) limits. While fundamental vibrational frequencies have been reported for OCN${}^{-}$ and SCN${}^{-}$ in the gas phase, only experimental vibrational frequencies of the salts for the heavier pnictogen analogues (P and As) have been reported. Experimental Raman vibrational frequencies for OCAs${}^{-}$ and SCAs${}^{-}$ salts were found to be coincidentally in good agreement with the CCSD(T) VCI frequencies near the CBS limit, differing by at most 13 cm${}^{-1}$ from the former and 9 cm${}^{-1}$ from the latter. These modest differences are likely due to the presence of counter-ions and other environmental effects in the solid state, and the overall agreement between the salts and gas-phase frequencies is quite similar to that observed for the OCP${}^{-}$ and SCP${}^{-}$ ions.

GRAPHICAL ABSTRACT

Keywords:

• Pnictogen-containing anions
• cyanate analogues
• anharmonic fundamental vibrational frequencies
• second-order vibrational perturbation theory (VPT2)
• vibrational configuration interaction (VCI) theory

Acknowledgments

This work is dedicated in memory of Dr. Timothy J. Lee, an exceptional theoretical chemist whose contributions left a profound mark on the field. A portion of the work presented here was accomplished thanks to the generous allocation of time on the computational resources available at Mississippi Center for Supercomputing Research (MCSR).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by the National Science Foundation (Division of Chemistry) under Grant CHE-2154403.