First-principles computation of the anharmonic vibrational spectra of sulfuryl halides SO2X2 (XÂ =Â F, Cl, Br)

Equilibrium geometries and anharmonic vibrational spectra of sulfuryl halides SO2X2 (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(OSO) and δ(X-S-X) deformation modes to 12-20 cm−1 for νa(SO), νs(SO), and νa(S-X) stretching modes. Wavenumbers of fundamental transitions of SO2F2 and SO2Cl2 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 SO2F2 and SO2Cl2 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 2ν1(2νa(SO)) and 2ν2(2νs(S-F)) modes of sulfuryl fluoride or 2ν2(2δ(OSO)) mode of SO2Cl2 and SO2Br2.