Vibrational spectra of halobenzene cations in the ground and (B)over-tilde 2B2 electronic states obtained by one-photon mass-analyzed threshold ionization spectrometry

Vibrational spectra in the ground electronic states, X B-2(1), of fluoro-, chloro-, bromo-, and iodobenzene cations and in the excited electronic states, B B-2(2), of chloro- and bromobenzene cations have been measured by mass-analyzed threshold ionization (MATI) via one-photon excitation with vacuum ultraviolet light. The spectra consist mostly of strong 0-0 bands and fundamentals, overtones, and combinations of totally symmetric a(1) modes. In particular, the observed vibrational bands in the B states have been assigned by referring to the assignments for the ionic ground states and those for the neutral molecules. From the MATI spectra, the ionization energies of fluoro-, chloro-, bromo-, and iodobenzene to the ionic ground states have been determined to be 74 229+/-5, 73 177+/-5, 72 570+/-5, and 70 638+/-5 cm(-1), respectively. The ionization energies to the B states have also been determined to be 91 404+/-5 and 85 822+/-5 cm(-1) for chloro- and bromobenzene, respectively. (C) 2002 American Institute of Physics.