Microwave spectrum of tetrolyl fluoride

Abstract

The microwave spectrum of the unstable molecule tetrolyl fluoride (but-2-ynoyl fluoride), CH₃—CC—COF, has been observed for the first time. The a-type rotational spectrum observed with a Stark-modulated microwave spectrometer is very dense, owing to internal rotation of the methyl group. The spectrum has also been measured in the frequency range 9–17 GHz using a pulsed-jet cavity microwave Fourier-transform (MWFT) spectrometer. Cooling in the jet has removed all internal rotation states other than |m|= 0 and |m|= 1, permitting assignment of the microwave spectrum. The threefold barrier to internal rotation has been confirmed to be very low [V₃= 2.20(12) cm^–1].