Molecular opacities of X¹Σ_g⁺、𝑎׳¹Σ_u^-、𝑎¹П_g and b¹П_u states for nitrogen molecule

Multi-reference configuration interaction (MRCI) approach with Davison size-extensivity correction (+Q) is employed to calculate the potential curves and dipole moments of X¹Σ_g⁺、𝑎׳¹Σ_u^-、𝑎¹П_g and b¹П_u states of N₂. The spectroscopic constants and vibrational energies are calculated and in excellent agreement with the available theoretical and experimental data. Based on the calculated molecular structure parameters, the opacities of N₂ at the temperature range (295K-20000K) under the pressure of 100 atms are presented. The results demonstrated that the wavelength range of absorption cross sections was enlarged with the temperature increasing. Moreover, the cross sections are mainly dominated in the range of ultraviolet for the cases with temperature T <5000K, while the obvious population can be found in the infrared ranges for the cases with temperature T>10000K due to the contribution of the excited states. The influence of temperature on the opacities of nitrogen molecule is investigated in the present work, which can provide theoretical and data support for astrophysics and nuclear weapons.