VACUUM-UV FLUORESCENCE SPECTROSCOPY OF PF3 IN THE RANGE 9-20 EV

The vacuum-UV and visible spectroscopy of PF3 using fluorescence excit ation and dispersed emission techniques is reported. The fluorescence excitation spectrum has been recorded following photoexcitation with m onochromatized synchrotron radiation from the Daresbury, UK source in the energy range 9-20 eV with an average resolution of similar to 0.01 5 eV. Transitions to the three lowest-energy bands in the Rydberg spec tra show resolved vibrational structure, they are assigned to transiti ons to the (8a(1))(-1) 4p, 5p, and 6p Rydberg states of PF3, and fluor escence is due to valence transitions in the PF2 radical. From a Franc k-Condon analysis of the vibrational structure, it is shown that the F PF bond angle in PF3 increases by similar to 14+/-1 degrees upon photo excitation. The use of optical filters shows that at least three excit ed electronic states of PF2 are responsible for the induced emission. Dispersed emission spectra in the UV/visible region have been recorded with an optical resolution of 8 nm at the BESSY 1, Germany synchrotro n source at the energies of all the peaks in the excitation spectrum. Four different decay channels are observed: (a) PF2 (A) over tilde(2)A (1)-(X) over tilde(2)B(1) fluorescence in the wide range 320-550 nm fo r photon energies around 9.8 eV, (b) PF2 (A) over tilde-(X) over tilde , and (B) over tilde(2)B(2)-(X) over tilde(2)B(1) fluorescence at simi lar to 300 nm for photon energies around 11.0 eV, (c) PF2 (C) over til de (2)A(1)-(X) over tilde(2)B(1) and (E) over tilde(2)B(1) ((2) Pi)-(A ) over tilde(2)A(1) fluorescence at similar to 222 and 325 nm, respect ively, for photon energies around 14.4 eV, and (d) PF A (3) Pi-X (3) S igma(-) fluorescence between 300-380 nm for photon energies around 16. 1 eV. These assignments are confirmed by action spectra in which the e xcitation energy of the vacuum-UV radiation is scanned with detection of the fluorescence at a fixed, dispersive wavelength. Using the singl e-bunch mode of the BESSY 1 source, we have attempted to measure the l ifetimes of the emitting states, but the timing profile of the source imposes an upper limit on lifetimes that can be measured of similar to 500 ns. We have therefore only been able to measure values for the be nt (C) over tilde(2)A(1) and linear (E) over tilde(2)B(1) ((2) Pi) sta tes of PF2 of 14.7 and 7.9 ns, respectively; the lifetimes of the othe r emitters are too long to measure by this method. Our assignments in PF2 are heavily dependent on recent ab initio calculations on the geom etries and energies of the valence electronic states of this species. Our knowledge on the electronic spectroscopy of this free radical is r eviewed. (C) 1998 American Institute of Physics. [S0021-9606(98)01603- 1].