Structure and analytic potential energy function of the molecules BeH, H2 and BeH2

Quadratic configuration interaction calculation (QCISD) and B3LYP methods have been used to optimize the possible ground-state structures of H-2, BeH and BeH2 Molecules. The results show that their ground electronic states are H-2 ((1)Sigma(g)), BeH ((2)Sigma) and BeH2((1)Sigma(g)); the stable structure of BeH2 Molecule is of D h symmetry. The Murrell-Sorbie potential energy function with 8 parameters of BeH and H-2 molecule has been derived from the least square method, according to which spectral data and force constants are deduced. The analytical potential energy function of BeH2 is derived from the many-body expansion theory. Since BeH, (D (infinity) (h)) formed from H + BeH has a deep potential trap, the complex com pound molecule of H-Be-H is easily formed. The reaction of Be + H-2 -> HBeH with Delta H = -1.4654 eV is an exothermic reaction.