STRUCTURES, STABILITIES AND IONIZATION-POTENTIALS OF NA(H2O)N AND NA(NH3)N (N=1-6) CLUSTERS - AN ABINITIO MO STUDY

The structure and stability of Na(H2O)n and Na(NH3)n (n = 1-6) have been calculated at the HF/3-21G level. For n greater-than-or-equal-to 4 Na(H2O)n is a surface complex, where Na atom tends to be situated on the surface of (H2O)n cluster. Na(NH3)n is an inclusion complex where Na is surrounded by NH3 molecules. Water-water hydrogen bonds play an essential role in stabilizing Na(H2O)n, whereas stabilization by Na-N bond formation is more important for Na(NH)n. Calculated ionization potentials as functions of n can reproduce qualitatively the experimentally found different trends between Na(H2O)n and Na(NH3)n, which are related to the above-mentioned different structural features.