Abstract
Photofragmentation of the chlorofluorocarbons, CF3Cl, CF2Cl2, and CFCl3, was investigated at 187, 125, and 118 nm using VUV harmonic generation techniques and (2+1) resonantly enhanced multiphoton ionization detection of ground Cl(2P3/20) and excited Cl*(2P1/20) state fragment atoms. Product translational energy and angular distributions were derived from Cl+ arrival time distributions obtained by time-of-flight mass spectrometry. Photolysis of CF3Cl at 125 and 118 nm takes place via the 4s(a1) and 4p(e) Rydberg states, respectively, and two primary fragmentation channels are observed. A ‘‘slow’’ channel with a most probable center-of-mass (c.m.) translational energy near zero is assigned to the production CF*3 radicals in the 2A′1, 2A″2, and 1E′ electronically excited states. The second Cl/Cl* fragmentation channel has a c.m. translational energy distribution peaked at Etr≥1 eV and is tentatively assigned to a sequential dissociation process in which rapid C–Cl single bond rupture is followed by a secondary fragmentation of CF*3 to CF2+F. The time-of-flight (TOF) spectra for CF2Cl2 and CFCl3 following excitation at 125 and 118 nm suggest that concerted three-body fragmentation involving the loss of two Cl/Cl* atoms is the dominant dissociation process. By contrast, photolysis of CF2Cl2 and CFCl3 at 187 nm results in structured Cl+ arrival time distributions which are used to derive translational energy distributions and asymmetry parameters. Simulations of the TOF spectra suggest the presence of three Cl/Cl* fragment channels, with the highest energy channel clearly attributable to single C–Cl bond rupture leading to internally excited molecular fragments. The contribution of sequential and simultaneous two-Cl loss processes to the low translational energy channels is also discussed.
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