In situ Radical Detection under Very Low Pressure Photolysis Conditions Using Resonance-Enhanced Multiphoton Ionization. Kinetics of CF3 Radicals Produced from IR Multiphoton Dissociation of Hexafluoroacetone

摘要

Resonance enhanced multiphoton ionization (REMPI) and mass spectrometry have been used to measure the kinetics of CF3 radicals inside of a very low pressure photolysis (VLPphi) cell. Infrared multiphoton dissociation (IRMPD) of hexa-fluoroacetone (HFA) is used to generate the radicals according to CF3COCF3 yields CF3 + CF3CO. REMPI spectra of vibrationally hot and thermalized CF3 radicals are presented. The absolute density of CF3 in the reactor is determined from the REMPI signal by using mass spectral data. This puts the calibration on the absolute basis necessary to treat competing unimolecular and bimolecular reactions of CF3 free radical. Measuring the CF3 density as a function of time between pulses of the IR laser and of HFA flow rate allows direct determination of the first-and second-order loss rates for CF3. The CF3CO radical is stable under our conditions and engages in recombination back to HFA at higher radical densities. Keywords: Acetones, Fluorine compounds, Carbon trifluoride, Reprints. (MJM)