Zero kinetic energy (ZEKE) photoelectron study of fluorobenzene-argon van der Waals complexes

Two kinds of van der Waals (vdW) complexes of fluorobenzene (FB) with argon, FB-Ar and FB-Ar-2, produced in supersonic jets were studied by mass-selected ion-current spectra and zero kinetic energy (ZEKE) photoelectron spectra by using two-photon resonant ionization through the first singlet electronic excited states (S-1). The results obtained from the ZEKE photoelectron spectra may be summarized as follows. (1) The adiabatic ionization energies have been determined as I-a(FB) = 74 238 +/- 4 cm(-1) (9.2043 +/- 0.0005 eV), I-a (FB-Ar) = 74 011 +/- 4 cm(-1) (9.1762 +/- 0.0005 eV), and I-d (FB-Ar-2) = 73 816 +/- 4 cm(-1) (9.1521 +/- 0.0005 eV). (2) The decreases in I-a have been found to be 227 and 422 cm(-1) for FB-Ar and FB-Ar-2, respectively, this fact indicating that the increases in the dissociation energy upon photoionization are 227 and 422 cm(-1), respectively. (3) Well-resolved vibrational progressions with frequencies of 12 and 9 cm(-1) have been observed for the vdW cations (FB-Ar)(+) and (FB-Ar-2)(+), respectively, and assigned to the vdW bending vibrations b(x)(+1) and b(xs)(+1), respectively, along the x axis (the C-F bond), by selecting some appropriate S-1 vdW vibrational levels as intermediate resonant states. (4) Two more bands appearing at 31 and 50 cm-l above the origin for (FB-Ar)(+) may be assigned to the vdW bending (b(y)(+2)) and the vdW stretching (s(z)(+1)), respectively. (5) From Franck-Condon calculations, it has been found that Ar is shifted by 7 degrees and 6 degrees for(FB-Ar)(+) and (FB-Ar-2)(+), respectively, with respect to their neutral S-1 states.