BINDING-ENERGIES OF CARBAZOLE-CENTER-DOT-S VAN-DER-WAALS COMPLEXES (S=N-2, CO, AND CH4)

Mass-selective ground-state vibronic spectra of molecular van der Waal s complexes carbazole S, S=N-2, CO, and CH4, were measured by stimulat ed emission pumping followed by resonant two-photon ionization of the vibrationally hot complexes. S-0-state vibrational modes were accessed from approximate to 200 cm(-1) up to the ground-state dissociation li mit D-0(S-0) of the van der Waals bond. Above D-0, efficient vibration al predissociation of the complexes occurs, allowing accurate determin ation of the van der Waals dissociation energies as 627.2+/-7.9 cm(-1) for N-2, 716.5+/-29.8 cm(-1) for CO, and 668.6+/-15.1 cm(-1) for CH4. In the S-1 excited state, the van der Waals binding energies increase to 678.5+/-8.0, 879.2+/-29.9, and 753.8+/-15.2 cm(-1), respectively. The relative increases upon electronic excitation are about 8% and 13% for N-2 and CH4, Similar to the analogous rare gases Ar and Rr. For C O, the relative increase of van der Waals binding energy is 23%. The d ifferences are primarily due to electrostatic interactions. (C) 1995 A merican Institute of Physics.