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Semi-empirical valence bond surfaces for the homonuclear alkali trimers (M3) have been obtained by evaluating the Coulomb and exchange integrals in the London equation, respectively, as half the sum and difference of new reliable analytical potential energy curves for the 1Σg+ and 3Σu+ states of the dimers (M2). Calculations were also carried out using an effective 3Σu+ universal diatomic function which was chosen to reproduce the experimentally known binding energy of Li3. The ground state equilibrium structures of those trimers are predicted to be an obtuse triangle (2B2 symmetry) bound with respect to M2(1Σg+)+M(2S) and ordered Li3>Na3>K3>Rb3>Cs3 according to their stabilities. The surfaces are found to be extremely flat with two saddle points, an acute isosceles triangle (2A1 symmetry) and a linear symmetric structure (2Σu+) lying above but very close to the minimum. The force constants of the 2Σu+, 2A1 and 2B2 structures, as well as the fundamental frequencies and zero point energies of vibration of the equilibrium 2B2 species, have also been calculated.

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'M2 systems (M', M = Li through Cs). The force constants and vibrational frequencies to stretching and bending of the optimal C2v 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'M2 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.

We report quasiclassical trajectory calculations for the reaction Li + Cs2 → LiCs + Li. The influence of the very pronounced mass differences of the colliding partners on the various dynamics attributes is investigated in detail. A remarkable linear dependence of the translational exothermicity as a function of the initial translational energy is observed, and rationalized using a hybrid statistical/stripping-spectator model.