Abstract
The first ethyl ester whose structure was determined by microwave spectroscopy is ethyl formate. It exists in two conformations. In the 1970s, that study was used as a model to determine the structures of other ethyl esters, ethyl cyanoformate, chloroformate, and trifluoroacetate. They display the same conformations as ethyl formate. But under the experimental conditions used, Stark modulation with a maximum electric field, static low pressure gas, rapid sweeping, and long detector time constants, each of those esters displays bands of an additional third species. A careful, high resolution study of ethyl cyanoformate only observed two conformers. A model has been proposed that the third species derives from a dense array of torsionally excited states with broadened transitions due to short lifetimes. The present study of ethyl trifluoroacetate in a pulsed jet Fourier Transform spectrometer is intended to clarify the earlier results. Two conformers are observed including all their monosubstituted 13C and 18O isotopologs. In a pulsed jet Fourier Transform spectrometer using argon as the carrier gas, only one conformer is observed. Switching to helium as the carrier gas, another, higher energy conformer is also observed.
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