Microwave spectrum of sulfur difluoride in the first excited vibrational states vibrational potential function and equilibrium structure

Microwave spectra of SF₂ in the first excited states of the three normal modes were observed and analyzed. A comparison of the observed inertia defects in the ν₁ and ν₃ states with those calculated by omitting the contributions of the Coriolis interaction between the two modes led to a $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ vibrational frequency differences of 25.72 ± 0.33 cm^?1, with ν₁ being definitely higher. The inertia defect in the ground state and our measured values for the inertia defect in the ν₂ state and for the $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ difference were combined with the centrifugal distortion constants of Kirchhoff et al. [J. Mol. Spectrosc.48, 157–164 (1973)] to improve the harmonic force field. The interaction constant between the two SF stretching coordinates was determined precisely. The third-order and the cubic anharmonic potential constants were calculated from the observed vibration-rotation constants. The equilibrium structure was determined to be $\text{r}{}_{\mathrm{e}}\text{(}\text{SF}\text{) = 1.58745 ± 0.00012}\text{A}\text{?}$ and θ_e(FSF) = 98.048 ± 0.013°.