			15min:

SIGNATURE OF CONFORMATIONAL RELAXATION IN THE MICROWAVE SPECTRUM OF ETHYL TRIFLUOROACETATE, (CF₃COO-CH₂CH₃).

NANCY S. TRUE, Department of Chemistry, University of California, Davis, CA 95616; ROBERT K. BOHN, Dept. of Chemistry, University of Connecticut, Storrs, CT 06269-3060.

Ethyl trifluoroacetate is a nearly prolate symmetric top, kappa = -0.95, which displays three series of a-type R-branch bands under low resolution conditions in a Stark-modulated spectrometer. Since the molecule exists in only two stable conformers, the origin of the third band series has remained a puzzle for thirty years. We show that the third band series arises from rotational spectra of species undergoing exchange between the two stable forms. This is a purely microwave analog of conformational relaxation which has been observed in NMR spectra under different time, potential energy, and rate regimes.