First-principles computation of the anharmonic vibrational spectra of sulfuryl halides SO 2X 2 (X = F, Cl, Br)

Abstract

Equilibrium geometries and anharmonic vibrational spectra of sulfuryl halides SO 2X 2 (X = F, Cl, Br) have been computed on MP2(frozen core) level of electronic structure theory in 6-31G(df) and effective core potential (ECP) Stevens–Basch–Krauss–Jasien–Cundari (SBKJC) SBKJC(3df) basis sets. Anharmonic spectra have been determined directly from MP2 potential energy surfaces using vibrational self-consistent field (VSCF) and correlation corrected vibrational self-consistent field (CC-VSCF) methods. Computed anharmonic corrections vary from 1.5 cm −1 for low frequency δ(O S O) and δ(X–S–X) deformation modes to 12–20 cm −1 for ν a(S O), ν s(S O), and ν a(S–X) stretching modes. Wavenumbers of fundamental transitions of SO 2F 2 and SO 2Cl 2 calculated in SBKJC(3df) basis are within 2–12 cm −1 of their experimental counterparts with RMSD of 7.7 and 7.3 cm −1, respectively. Anharmonic spectra of SO 2F 2 and SO 2Cl 2 computed in 6-31G(df) basis are farther apart from experiment having RMSDs of 17.2 and 15.0 cm −1. Overtone transitions with observable infrared intensity (above 0.5 km/mol) are attributable to 2 ν 1(2 ν a(S O)) and 2 ν 2(2 ν s(S–F)) modes of sulfuryl fluoride or 2 ν 2(2 δ(O S O)) mode of SO 2Cl 2 and SO 2Br 2.