THE VACUUM-ULTRAVIOLET PHOTODISSOCIATION OF THE CHLOROFLUOROCARBONS -PHOTOLYSIS OF CF3CL, CF2CL2, AND CFCL3 AT 187, 125, AND 118 NM

Photofragmentation of the chlorofluorocarbons, CF3Cl, CF2Cl2, and CFCl 3, was investigated at 187, 125, and 118 nm using VUV harmonic generat ion techniques and (2 + 1) resonantly enhanced multiphoton ionization detection of ground Cl(2P3/2(0)) and excited Cl(2P(1/2)0 ) state frag ment atoms. Product translational energy and angular distributions wer e derived from Cl+ arrival time distributions obtained by time-of-flig ht mass spectrometry. Photolysis of CF3Cl at 125 and 118 nm takes plac e via the 4s(a1) and 4p(e) Rydberg states, respectively, and two prima ry fragmentation channels are observed. A ''slow'' channel with a most probable center-of-mass (c.m.) translational energy near zero is assi gned to the production CF3 radicals in the 2A1', 2A2'', and 1E' elect ronically excited states. The second Cl/Cl fragmentation channel has a c.m. translational energy distribution peaked at E(tr) greater-than- or-equal-to 1 eV and is tentatively assigned to a sequential dissociat ion process in which rapid C-Cl single bond rupture is followed by a s econdary fragmentation of CF3 to CF2+F. The time-of-flight (TOF) spec tra for CF2Cl2 and CFCl3 following excitation at 125 and 118 nm sugges t that concerted three-body fragmentation involving the loss of two Cl /Cl atoms is the dominant dissociation process. By contrast, photolys is of CF2Cl2 and CFCl3 at 187 nm results in structured Cl+ arrival tim e distributions which are used to derive translational energy distribu tions and asymmetry parameters. Simulations of the TOF spectra suggest the presence of three Cl/Cl fragment channels, with the highest ener gy channel clearly attributable to single C-Cl bond rupture leading to internally excited molecular fragments. The contribution of sequentia l and simultaneous two-Cl loss processes to the low translational ener gy channels is also discussed.