Fluorescence excitation spectroscopy of some haloethenes, CF2 = CXY (XY ≡ FCl, Cl2, FH), excited in the vacuum ultraviolet (70–180 nm) Original Research Article

The fluorescence excitation spectra for three haloethenes, C2F3H, C2F2Cl and C2F2Cl2, have been measured in a molecular beam using synchrotron radiation in the range 70–180 nm as the excitation source. These results extend previous studies on the fluorescence excitation spectrum for C2F3Cl to shorter wavelengths (< 105 nm) and present the first such results for C2F3H and C2F2Cl2. The spectra show a series of well defined Rydberg progressions converging to the first and second ionisation potentials superimposed upon continuous and broadly structured features that correspond to valence transitions. Vibrational structure is seen for features at energies below the first ionisation potential but not above. As no absorption spectra have been reported for these molecules for wavelengths less than ≈105 nm, the spectra are analysed with reference to photoelectron and electron impact spectroscopic studies on these molecules.