Absorption and Laser-Excited Fluorescence Spectra of Matrix-Isolated Metal van der Waals Dimers

For the past 10 years the study of diatomic van der Waals species has accelerated rapidly [l-451. These molecules possess only a very weakly bound ground state with no formal chemical bonding. The depth of the potential well, defined only by van d e r Waals forces, is typically less than 2000 cm−1 (0.25 eV or 5 .72 kcal/mole). However, upon excitation of an antibonding electron to a bonding orbital, several lowlying excited states are expected to be chemically bound. Commonly referred to as excimers (excited state dimers), these molecules are found for atoms from Group IIA (alkaline earth), Group IIB, and Group 0 (rare gases), whose valence electrons constitute a closed shell.