Research on the Physical Properties of Nitrogen Molecules and Ions in External Electric Fields

As the primary constituent of Earth's atmosphere, N₂ and its ion N₂⁺ directly influence the atmosphere's chemical composition and physical properties; therefore, studying their physical behavior in electric fields is of significant importance. Based on density functional theory (DFT) using the B3LYP functional and the 6-311G+(d) basis set, this study systematically investigates the changes in physical properties—such as bond length, total energy, energy level distribution, infrared spectra, and tunneling effect—of N₂ molecules and N₂⁺ ions under an external electric field (0–0.03 a.u.) applied perpendicular to the N–N bond axis. The results show that as the electric field strengthens, the bond length of the N₂ molecule exhibits step-like changes, while that of N₂⁺ increases continuously without step behavior. Meanwhile, the total energy of N₂⁺ gradually decreases, the dipole moment increases steadily, the energy gap of Alpha orbitals narrows, and that of Beta orbitals widens. Its infrared absorption intensity enhances significantly with a red shift, and changes in frontier orbital energies further reveal shifts in electron cloud distribution and alterations in wave function phase differences. The study also analyzes the external field-induced tunneling effect in N₂ molecules and their transition to N₂⁺, as well as the evolution trends of potential energy curves for both species under strong field conditions (0–0.08 a.u.). This work provides a theoretical basis for the microscopic behavior mechanisms of nitrogen in electric fields and offers important reference value for related fields such as atmospheric electricity and plasma physics.