PHOTON FRAGMENT-ION COINCIDENCE INVESTIGATION OF THE CONTINUOUS ULTRAVIOLET EMISSIONS PRODUCED BY FAST-ION IMPACT ON CF4 AND CHF3

A continuous or quasicontinuous band in the 200-500 nm wavelength rang e is known to be emitted following electron, fast ion, and vacuum ultr aviolet photon impact on CF4 and CHF3. We performed a photon/fragment- ion coincidence experiment following 2 MeV H+, He+, and He++ impact on CF4 and CHF3 with the objective to clarify the nature of the emitter and to study the dynamics of the emission process. In the case of the CF4 molecule, we observed that the photons in the 200-500 nm range are quantitatively coincident with CF3+ fragments. From the structure of the coincidence peak, we derived the kinetic energy released during th e dissociation process and compared it with the optical spectrum and t he total available energy. It follows that the CF3+ ions are vibration ally and/or rotationally highly excited. The continuous emission is ex plained by a radiative decay of the CF4+(C 2T2) state to the CF4+(X 2A 1) repulsive potential surface which dissociates quickly into CF3+ and a fluorine atom. In the case of the CHF3 molecule, we observed coinci dences between photons in the 200-500 nm range and CHF2+ fragments. A process similar to that in the CF4 molecule seems to take place with t he CHF3+(D) state as the precursor. In the same spectral range, a band of electronically excited CF2 radicals seems also to be present. No coincidences between photons in the 200-500 nm range and CF3+ were obs erved which excludes the CF3+ as a precursor of the continuous bands in the case of CHF3 and makes it very unlikely in the case of CF4.