Vacuum UV spectroscopy and dynamics of CHF3: analysis of emissions and evidence for parent ion emission

The fluorescence observed following electron impact and vacuum UV photon excitation of fluoroform (CHF 3 ) are studied using three techniques: (a) electron beam excitation of a supersonic molecular beam with dispersed fluorescence detection; (b) He* and Ne* rare-gas metastable excitation at room temperature with dispersed fluorescence detection; (c) photon excitation at room temperature using tunable vacuum UV radiation from a synchrotron source with undispersed fluorescence detection. Using the first two techniques, the spectra are dominated by CF 2 Ã-[Xtilde] fluorescence. The spectra are continuous owing to the high density of rovibrational transitions, but a vibrational progression in the bending mode is observed in the rare-gas metastable experiment at high gas pressure. Using photons in the energy range 11-35 eV, three distinct fluorescence decay channels are observed: (1) CF 3 fluorescence for photon energies 11-13 eV; (2) CF 2 fluorescence for energies 14-18 eV; (3) CHF + 3 fluorescence for energies greater than 20 eV. The shapes of the excitation functions confirm that (1) and (2) are resonant processes via Rydberg states of CHF 3 , but (3) is a non-resonant photoionisation process. The emitting state in CHF + 3 is the [Dtilde] 2 A 1 state, with a vertical ionisation potential of 20·5 eV. Using the synchrotron in its single-bunch mode, radiative lifetimes of the fluorescing electronic states of CF 3 , CF 2 and CHF + 3 have been measured to be 17, 52 and 80 ns respectively.