Semiempirical valence bond potential energy surfaces for the alkali trimers

Semiempirical valence bond calculations based on a modified LEPS method which have been reported previously for the potential energy surfaces of the homonuclear alkali trimers are now extended to the M′M 2 systems (M′, M = Li through Cs). The force constants and vibrational frequencies to stretching and bending of the optimal C 2v structures for the trimers have been calculated, and the geometries of such structures rationalized on the basis of Walsh-type diagrams. With basis on the simple molecular orbital theory, it is predicted that the ESR spectra of the M′M 2 trimers may show dramatic differences depending on whether the two equal atoms are heavy (i.e., LHH or type I) or light (HLL; type II). However, for all members of a given type, the ESR are predicted to be similar, irrespectively of the specific atoms involved.