Ab initio MO studies of van der Waals molecule (N-2)(2): Potential energy surface and internal motion

摘要

The equilibrium structure, potential energy surface and van der Waals (vdW) mode vibration of (N-2)(2) have been studied with high levels of ab initio calculations. The most stable structure is found to be a 45 deg. canted parallel structure of C-2h. On the other hand, neither T-shape of C-2v nor cross-shape of D-2d is a stable structure, but they are transition state structures, which are contrary to the previous calculations. The out-of-plane motion changing from the 45 deg. canted parallel structure of C-2h to the cross-shape of D-2d has a higher barrier than the in-plane motion. The binding energy of two N-2 monomers is about 80 cm(-1) and the fundamental frequency of vdW stretching mode is estimated at 22 cm(-1). A small energy difference of 5 cm(-1) between the C-2h and C-2v structures implies that two N2 molecules move coherently like a gear rotation in the plane. This internal freedom of motion should make the rotational energy states extremely modulated, and therefore, a very complex spectrum pattern could be expected. (C) 1998 American Institute of Physics. [S0021-9606(98)31044-2]. [References: 13]