Theoretical study of rectangular (D2h) N4

Abstract

The N ₄ 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 N ₄ 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 N ₂ molecules. The barrier towards dissociation to 2N ₂ from (D _2h ) N ₄ is calculated to be 2.5 kcal mol ⁻¹ , which is much less than the corresponding value for tetrahedral N ₄ . It is, however, sufficient to render (D _2h ) N ₄ stable at room temperature. At the same level of theory, the quadratic (D _4h ) N ₄ is not stable. It is found to be a saddle point of second order.