The Determination of the Potential Constants of SO2 from Centrifugal Distortion Effects

The microwave spectrum of SO2 was reanalyzed with particular emphasis upon the effect of centrifugal distortion. It was possible to fit the rotational spectrum to within a mean deviation of ±0.23 Mc using the energy expression given by Kivelson and Wilson. The rotational constants so determined are a=60778.79 Mc, b=10318.10 Mc, and c=8799.96 Mc. The four distortion constants could not be uniquely determined directly from the rotational spectrum. The sets of potential constants determined by Wilson and Polo were used to calculate distortion constants and these in turn used to calculate frequency shifts due to centrifugal distortion. These shifts are critically dependent upon the set of potential constants used. By choosing a set of potential constants compatible with the infrared spectrum which also yield distortion frequency shifts in accord with those obtained from a direct analysis of the rotational spectrum, a very sensitive determination of the potential constants may be made. The resulting force constants are: fd=10.006×105 dyne cm—1; fα/d02=0.7933×105 dyne cm—1; fdd=0.0236×105 dyne cm—; fdα/d0=0.189 dyne cm—.