ABINITIO AND MONTE-CARLO STUDY OF THE STRUCTURE AND STABILITY OF H3+(H2)N (N = 3-16)

The molecular geometries of hydrogen cluster ions, H-3+(H-2)n (n = 3-16), were investigated by using the classical Monte Carlo and annealing method. The two-body potential functions were obtained by fitting the results of ab initio MP4(SDTQ) calculations. Molecular structure and stability are mainly determined by an ionic interaction between H-3+ and H-2. The H-2-H-2 interaction forces H-2 molecules to stay away from each other but seems to have little effect upon the structure and stability of clusters in the vicinity of the equilibrium structure. The n dependency of the binding energy (-DELTA-E(n-1,n)) is in good agreement with the experimental trend in -DELTA-H(n-1,n) known for n less-than-or-equal-to 9. Magic numbers in the stabilization energy have been found at n = 3, 6, 9, 12, and 15, where optimized molecular structures are closed shells with 3-fold symmetry and have one to five layers of (H-2)3 solvation shells over the H-3+ core.