Centrifugal distortion analysis of microwave spectra of asymmetric top molecules. The microwave spectrum of pyridine

Abstract

Several microwave investigators have experienced the great difficulties involved in the determination of the six linearly independent constants appearing in the first-order treatment of the centrifugal distortion effect. Ambiguity specially arises when dealing with the A 1- A 6 constants introduced by Kivelson and Wilson. The problem can be partly solved by proper selection between the possible sets of constants, the choice depending on the degree of asymmetry and the collection of transitions present. The suggested methods are tested on the remeasured spectrum of pyridine, on the earlier measured lines of furan including some new high- J Q-branch transitions, and on the spectra of dimethyl sulfide and dimethyl sulfoxide reported in the literature. In an appendix is shown that the results obtained for the nonplanar molecules are in agreement with a recent theoretical development by Watson.