| Popis: |
The lifetimes of the zeroth and some vibiationally excited levels of the B(π-1) states of the radical cations of hexafluorobenzene (1), pentafluorobenzene (2), 1,2,3,4- (3), 1,2,3,5- (4) and 1,2,4,5-(5)-tetrafluorobenzene, 1,3,5- (6) and 1,2,4- (7)-trifluorobenzene in the aaseous phase have been measured. The cations were produced by 20—30 eV electron beam excitation of the samples at pressures < 10-3 torr The 00 level lifetimes (± 2 ns) found were 1 -48 us, 2 -47 ns, 3 - 50 ns, 4 - 50 ns, 5 - 30 ns, 6 - 58 os and 7 - 10 ns. The emission of 1,3-difluoralienzene radical cation (8) has also now been detected and the emission spectra of the fluorobenzenes 1-8,B → A, X band systems, are discussed. The emission intensities of the B →A, X transitions have been determined for 2-8 relative to 1. The lack of detectable emission from the corresponding excited (ir1) states of the radIcal cations of 1,4-and 1,2-difluorobeozene, fluorobeuzene, besizene and benzene-d6 indicates that the quantum yields of emission are < 10-5. The implications of the positive and negative results are considered with respect to the electronic structures of these species and the possible non-radiative pathways accessible to such excited cations. |
