Structure and potential energy surface for Na+center dot N-2

Attention is focused on the Na+. N-2 complex as part of a study of Na+-cont aining complexes, which have been implicated in the formation of sporadic s odium layers in the upper atmosphere. The equilibrium structure is found to be linear, in agreement with previous studies. A potential energy hypersur face is calculated at the CCSD(T)/aug-cc-pVTZ level of theory, where the N- 2 moiety is held fixed, but a wide range of Jacobi bond lengths and bond an gles are sampled. This hypersurface is fitted to an analytic form and from this anharmonic vibrational separations are calculated, and compared to har monic values. Rovibrational energy levels are also calculated from the fitt ed hypersurface. The best estimate of the interaction energy, Delta E-e is 2770 cm(-1), and Delta H-f(298)(Na+. N-2) = (136.5 +/- 2.0) kcal mol(-1). ( C) 1999 American Institute of Physics. [S0021-9606(99)30632-2].