Photoionization of lithium chloride vapors: the structure and stability of alkali halide molecules and ions

Photoionization yield curves near threshold are reported for Li+, LiCl+, Li2C+ (Li2Cl2) and [Math] value of 4.77g eV is deduced for D0(LiCI). The adiabatic ionization potentials obtained for LiCl (9.6 eV) and Li22Cl2 (10.2 eV) agree with earlier photoelectron spectroscopic measurements. The value deduced for Li3Cl3 (10.17 eV) is not significantly different from that for Li2Cl2 The structure and binding energies of these and other alkali halide molecules and ions have been examined by using five different models of ionic interaction previously proposed. The more sophisticated (Rothberg and Brumer-Karplus) models provide good agreement with experiment for M2X2 (and perhaps M3X3) neutral species, but the Brumer-Karplus model is unsatisfactory for the M2X+ and [Math] ions. These two models generally predict linear M2X+ structures, whereas the Rittner and Mohammad models generally predict bent structures. Xu calculations based on geometries provides by these models predict a lower ionization potential for the trimers of lithium fluoride and lithium chloride than the corresponding dimers, whereas a Hartree-Fock calculation arrives at the opposite trend for lithium fluoride. The binding energies and geometric structures of the various alkali halide molecules and ions computed by these ionic models are tabulated.