Infrared spectrum and theoretical calculations of a higher-energy isomer of the CO–SO2 complex

Abstract

The rovibrational spectrum of the CO–SO₂ complex is measured in the CO fundamental region by direct absorption in a supersonic slit jet expansion. Two new vibrational bands are assigned to CO–SO₂, and the observed transitions are analyzed using the standard Watson S-reduced asymmetric-top Hamiltonian. The band origin is observed at 2150.95502(18) cm⁻¹ for band I and 2148.24081(39) cm⁻¹ for band II, which shows a blue shift from that of the CO monomer by about +7.684 cm⁻¹ and +4.753 cm⁻¹, respectively. Band I is an ordinary a/c hybrid vibrational band, while only a-type transitions with even-K_a levels are observed in band II. A restricted 2-dimensional intermolecular potential energy surface (2D-IPES) is constructed at the MP2/aug-cc-PVTZ level of theory. Full geometry optimizations and harmonic frequency calculations are performed for stationary points on the 2D-IPES. Band I is attributed to the most stable C-bonded isomer of CO–SO₂. Band II is attributed to a higher-energy O-bonded isomer with a vibrationally averaged planar structure of C_2v symmetry.