Properties of the binding in 12-group homonuclear dimers from excitation and fluorescence spectra

Abstract

Excitation and fluorescence ultraviolet spectra of 12-group homonuclear metal dimers (i.e., M 2 , where M=Zn, Cd and Hg) recorded at several molecular transitions provide information on interatomic potentials of the ground and low-lying excited electronic energy states of the dimers. In experiments the molecules were produced in a supersonic beam and were excited in a vacuum chamber using a dye-laser beam. Well-resolved vibrational structures in excitation spectra, isotopic and rotational structures of the vibrational components, as well as Condon internal diffraction patterns in the fluorescence bands were recorded and analyzed. Analyses of the excitation spectra lead to the analytical representations of the ground- and excited-state interatomic potentials. Analyses of the fluorescence profiles yielded information on the repulsive parts of the ground-state interatomic potentials. In the case of Cd 2 and Hg 2 , the results confirm a relatively soft repulsion between two metal atoms in the short-range region of internuclear separation and make allowance for a theoretically predicted covalent admixture to the ground-state van der Waals binding. The hypothesis needs further corroboration. The determined interatomic potentials of mercury dimers were used in a proposed mechanism of vibrational cooling in translationally cold Hg 2 .