Asymmetric structure and force field of the 1B2(1A′) state of sulphur dioxide

Abstract

The vibrational term values, principal rotational constants and centrifugal distortion constants of the ¹ B ₂ state of SO₂ at 42 573 cm^-1 (2350 Å) ‡ 1 Å = 10^-10 m. 1 d = 1 dyne = 10^-5 N. 1 u = 1 unified atomic mass unit ≈ 1·660 531 × 10^-27 kg. View all notes are interpreted in a unified treatment using (i) a vibrational hamiltonian based on a double minimum potential in the antisymmetrical stretching coordinate q ₃ and strong anharmonic coupling of q ₃ with the symmetric stretch q ₁; and (ii) a modified treatment of Coriolis coupling and centrifugal distortion, in order to take account of the irregular intervals in the vibrational manifold. This treatment successfully explains a group of observed quantities, including isotopic data, relative intensities and inertial defects, which were not used in determining the constants of the potential function. The analysis indicates that there is a double minimum potential in the antisymmetric mode with a barrier of about 141 cm^-1 at the C _2v configuration; the top of the barrier is probably significantly higher, by 43±20 cm^-1, than the zero-point vibrational level, corresponding to an asymmetrical structure in this electronic state. Calculated equilibrium values of the short and long distances are respectively 1·491 and 1·639 Å.