Microwave Spectrum of Fluoroacetone

Abstract

The microwave spectrum of fluoroacetone has been studied in the region 18–35 GHz, and transitions arising from one rotamer have been assigned. This rotamer has all the heavy atoms in a plane with the fluorine and oxygen atoms trans to one another. The rotational constants are A = 8658.06, B = 4021.64, and C = 2845.12 MHz, which give Ia + Ib − Ic = 6.406 amu·Å2. Stark effect measurements give the dipole-moment components: μa = 0.907 ± 0.020 D, μb = 0.76 ± 0.05 D, μ = 1.18 ± 0.05 D. Satellite lines arising from excited states of both the methyl and CH2F torsions have been identified. The splittings of the rotational lines into A and E components have been analyzed using as a model a rigid methyl group attached to a rigid framework. This treatment gives a barrier to internal rotation of the methyl group of 1488 ± 30 cal/mole for the ground state and 1467 ± 30 cal/mole for the first excited methyl state. A model which takes into account coupling of the −CH3 and −CH2F torsional vibrations is also considered.