Observation of new electronic states of the Al–H 2/D 2 complex

Abstract

A study of the electronic spectra of the weakly bound Al–H 2 and Al–D 2 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–H 2/D 2 stretch vibrational mode associated with the strongly bound 2 B 2 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)–H 2 state. A Franck–Condon analysis was carried out to derive an effective one-dimensional potential energy curve for the van der Waals stretch coordinate in the excited 2 B 2 state. This potential energy curve is compared with the previously computed one-dimensional C 2v cut for this state [Faraday Discuss. 118 (2001) 387]. 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–H 2 Rydberg states are compared with the computed binding energy of the ionic Al +–H 2 complex.