HIGH-RESOLUTION MID-IR MOLECULAR ABSORPTION-SPECTROSCOPY OF COLLISIONALLY COOLED HYDROFLUOROCARBON VAPORS

Rotationally and vibrationally cooled (below 100 K) high resolution (u p to 0.004 cm(-1)) mid-IR gas-phase spectra of three hydrofluorocarbon s [difluoromethane (CH2F2), trifluoromethane (CHF3) and 1,1,1-trifluor oethane (CH3CF3)] have been obtained using a Bruker IFS 120HR Fourier transform spectrometer and a collisional cooling (or 'diffusive trappi ng') technique at the Laboratory Spectroscopy Facility of the Rutherfo rd Appleton Laboratory. To demonstrate the applicability of this techn ique to the simplification of dense molecular absorption features, the collisionally cooled spectra are compared with higher resolution (up to 0.0016 cm(-1)) measurements of the gases in conventionally cooled g as cells at 296 and 200 K. The suppression of thermally populated vibr ational states in the collisionally cooled spectra was particularly ev ident. The advantages of this technique over supersonic jet spectrosco py are discussed. Spectral features arising from the formation of hydr ofluorocarbon molecular clusters were also observed.