Vacuum-ultraviolet photoexcitation of some non-metal halides
The vacuum-ultraviolet (VUV) fluorescence spectroscopy of CX\(_2\)Y\(_2\) (X, Y = H, Cl or Br) has been studied following gaseous photoexcitation in the range 9-22 eV using synchrotron radiation. Fluorescence excitation, dispersed emission and action spectra have been recorded to probe the molecule in this way. Photoexcitation of these molecules has resulted in the population of Rydberg states of the neutral molecule and outer valence states of the parent ion. The study has shown that the emitters in the range 190-690 nm are due to either, neutral fragments formed by dissociation of Rydberg states of the neutral molecule or excited states of the parent ion. The identity of some of the dominant dissociation channels have also been identified via. appearance potentials extracted from action spectra. The threshold photoelectron photoion coincidence (TPEPICO) spectroscopy of CX\(_2\)Y\(_2^+\) (X, Y = H, Cl or Br), SeFe\(_6^+\), TeF\(_6^+\), SF\(_5\)CF\(_3^+\) and SF\(_5\)Cl\(^+\) has been studied following gaseous photoexcitation in the range ca. 12-27 eV using synchrotron radiation. The identity of some of the dominant dissociation channels have been identified in a similar way in which the information is extracted from action spectra in fluorescence spectroscopy. Appearance potentials extracted from ion yield plots have allowed comparison with known calculated thermochemistry. Measurement of fixed-energy TPEPICO spectra have been used to determine the decay dynamics of some two-bodied ionic dissociations. Finally, using a variation of TPEPICO spectroscopy, the kinetic energy released into certain fragments over a range of energies has been determined. Using an impulsive model, the data has been extrapolated to zero kinetic energy to obtain a value for the first dissociative ionisation energy of these molecules. From this value, more thermochemical data has been inferred.