Which Is the Highest Occupied Molecular Orbital: HOMO of N₂σ type or π type?

Abstract

The nitrogen molecule N₂has been regarded as a triple-bonded homonuclear diatomic molecule in many textbooks of physical chemistry. However, the character of the highest occupied molecular orbital HOMO (σ type or π type) is controversial in those textbooks. In this note, using RHF/6–311++G** calculation we show that the HOMO of N₂is π type in the region close to the equilibrium (1.0703 Å ). In the region where the bond length is larger than 1.045 Å , the HOMO of N₂is not σ type but π type.