Theoretical study of rectangular (D_2h) N₄

Abstract

The N₄ molecule in a rectangular geometry (D_2h) has been studied by means of ab initio calculations based on the GAUSSIAN 94 computer code. Whereas various single configuration approaches adequately described N₄ at its equilibrium geometry, a multiconfigurational approach, such as the complete active space SCF, was required to describe the transition-state region and the dissociation to two N₂ molecules. The barrier towards dissociation to 2N₂ from (D_2h) N₄ is calculated to be 2.5 kcal mol⁻¹, which is much less than the corresponding value for tetrahedral N₄. It is, however, sufficient to render (D_2h) N₄ stable at room temperature. At the same level of theory, the quadratic (D_4h) N₄ is not stable. It is found to be a saddle point of second order.