15min:

XIAOFENG TAN, PAUL J DAGDIGIAN, Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685.

A study of the electronic spectra of the weakly bound Al-H₂ and Al-D₂ complexes is presented. The complexes were generated in a pulsed, free-jet supersonic beam and detected with laser fluorescence excitation and depletion spectroscopy. All observed excited vibronic levels predissociate, and the transitions were detected by observation of lower-energy, emitting Al atoms. A long excited-state progression in the Al-H₂/D₂ stretch vibrational mode associated with the strongly bound ²B₂ electronic state correlating with the Al(3d) atomic asymptote was observed. The Lorentzian widths of these bands are large, indicative of strong coupling to the repulsive Al(4s)-H₂ state. A Franck-Condon analysis was carried out to derive an effective 1-dimensional potential energy curve for the van der Waals stretch coordinate in the excited ²B₂ state. This potential energy curve is compared with the previously computed 1-dimensional C_2v cut for this state. Bands associated with the mixed 5d, 6s 3p electronic transition are also reported. A complex of pattern of vibronic energies was observed, and the Lorentzian widths of these bands vary greatly. The binding energies of these and other Al-H₂ Rydberg states are compared with the computed binding energy of the ionic Al⁺-H₂ complex.