Comprehensive vacuum ultraviolet photoionization study of the CF3• trifluoromethyl radical using synchrotron radiation

Abstract

The trifluoromethyl radical, CF(3)(●), is studied for the first time by means of threshold photoelectron spectroscopy (TPES). The radical is produced in the gas phase using the flash-pyrolysis technique from hexafluoroethane as a precursor. CF(3)(+) total ion yield and mass-selected TPES of the radical are recorded using a spectrometer based upon velocity map imaging and Wiley-McLaren time-of-flight coupled to the synchrotron radiation. The high resolution of the instrument and of the photons allows the observation of rich vibrational progressions in the TPES of CF(3)(●). By using Franck-Condon factors computed by Bowman and coworkers, we have been able to simulate the TPES. The initial vibrational temperature of the radical beam has been evaluated at 350 ± 70 K. The structures have been identified as transitions between (n(1),n(2)) and (n(1)(+),n(2)(+)) vibrational levels of CF(3) and CF(3)(+) with small excitation of the breathing mode, ν(1)(+) (,) and large excitation (n(2)(+) = 10-26) of the umbrella mode, ν(2)(+), in the cation. From the energy separation between the two resolved peaks of each band, a value of 994 ± 16 cm(-1) has been derived for the ν(1)(+) breathing frequency of CF(3)(+). For the high-lying n(2)(+) levels, the apparent ν(2)(+) umbrella spacing, 820 ± 14 cm(-1), is fairly constant. Taking into account the ν(2)(+) anharmonicity calculated by Bowman and coworkers, we have deduced ν(2)(+) = 809 ± 14 cm(-1), and semi-empirical estimations of the adiabatic ionization energy IE(ad.)(CF(3)(●)) are proposed in good agreement with most of previous works. A value of the vertical ionization potential, IE(vert.)(CF(3)(●)) = 11.02 eV, has been derived from the observation of a photoelectron spectrum recorded at a fixed photon energy of 12 eV.