Resonance between the ground vibrational state and the lowest frequency bending mode of thioketene

Far-infrared and mid-infrared spectra of thioketene have been recorded over the region 200-1250 cm^-1 and transitions assigned from the ν₄, ν₅, ν₆, and ν₉ fundamentals and ν₅ + ν₉ ← ν₉ and ν₅ + ν₆ ← ν₆ hot bands. Ground state combination differences from ν₄ and ν₅, together with ν₆ and ν₉ transitions, lower state combination differences from the ν₅ + ν₉ ← ν₉ and ν₅ + ν₆ ← ν₆ hot bands, and previous millimeter-wave data, have been included in a combined fit of ν₆, ν₉, and the ground state. The strong a-axis Coriolis interaction between ν₆ and ν₉ has been treated along with the c-axis centrifugal distortion interaction between ν₉ and the ground state. The magnitudes of these interactions are in agreement with values obtained from ab initio molecular orbital calculations at the MP2/6-311G** and CCSD/6-311G** levels of theory.