ON THE INTERPRETATION OF THE PURE ROTATION SPECTRUM OF FLUOROFORM IN EXCITED VIBRATIONAL $STATES^{\ast}$

Abstract

Some of the $anomalies^{1}$ reported in the pure rotation spectrum of fluoroform in the excited vibrational state $v_{6}=1$ can be explained with the assumption that the two unperturbed levels $K=0, l_{6}= \pm 1$ and $K = \pm 2, l_{6} = \pm 1$ lie very close to each other. The coupling between these two levels due to l-type resonance is then much stronger than usual. This is a good example of the situation previously described as ``accidentally strong essential $resonance''^{2}$. $^{\ast}$Supported in part by the Air Force Cambridge Research Laboratories O.A.R. $^{1}$ C. C. Costain, J. Mol. Spectroscopy, 9, 317 (1962). $^{2}$ G. Amat and H. H. Nielsen, J. Chem. Phys. 36, 1859 (1962).