Infrared–radiofrequency double-resonance spectra and pressure broadening in the enantiomers and racemic mixture of gaseous 1,2-dichloro-2-fluoroethanone

Abstract

The frequencies and pressure broadening of some infrared–radiofrequency double-resonance absorptions are reported for the (–) enantiomer and racemic mixture of 1,2-dichloro-2-fluoroethanone at mTorr pressures. This is the first study of its kind, aimed at discerning spectral differences between an enantiomer and its racemic mixture at sub-Doppler resolution. The different frequency dependence of the lineshape in the enantiomer and racemic mixture as a function of pressure (i.e. collision rate) is a source of information on the statistical cross-correlation between vibration, rotation and translation during the intermolecular collision. Some differences in intensity have been found for the infrared–microwave double-resonance lines at 736 and 588 MHz on the 10 R32 CO₂ laser line, but these differences could be due to chemical and/or absorption phenomena or to a genuine intensity difference between the enantiomer and the racemate. Another radio-frequency resonance at 273 MHz was also investigated and the results are given in this paper together with their equivalents in all three lines in the racemic mixture. This high-resolution spectroscopic investigation does not show with a clear level of confidence the differences expected from the different statistical correlation between vibration, rotation and translation in enantiomer and racemic mixture.