Interatomic potentials for van der Waals complexes of group 13 metal atoms: AlAr, AlKr, and AlXe

Abstract

Interatomic potential parameters for the ground X1,2 2Π1/2,3/2 and excited B 2Σ+1/2 states of jet-cooled van der Waals complexes of Al atoms with rare gases have been determined from fluorescence excitation and emission spectra. Vibrational numbering in the B states is established from isotopic and rotational broadening of fluorescence excitation line shapes. Bond distances are estimated by comparison with analogous states of alkali–rare gas molecules, and by modeling observed relative emission intensities with calculated Franck–Condon factors. Morse potentials are found to adequately describe the data for the ground states, but for the excited states there are indications of departures from Morse functions at large internuclear distances. Dissociation energies De are estimated from Birge–Sponer extrapolations. Multiplet splittings in Al–rare gas complexes are compared to those in In–rare gas complexes and are discussed in terms of an empirical treatment of spin–orbit coupling, which assumes that the spin–orbit coupling constant for the molecule is the same as that for the atom. The ground X1 state of each Al–rare gas molecule is more stable than that of the analogous In complex, whereas the spin–orbit excited X2 state is less stable. This is explained by the greater mixing between the X1 state and the dissociative A 2Σ+1/2 state for indium over aluminum, caused by the greater spin–orbit coupling constant for the heavier metal.