Molecular opacities of low-lying states of oxygen molecule

The X³Σ_g^-, A'³△_u, A³Σ_u⁺, 1³Π_g, and B³Σ_u^- electronic states of oxygen molecule (O₂) are calculated by the multiconfiguration self-consisted filed (MRCI) + Q method with the scalar relativistic correction and core-valence correlation correction. The obtained spectroscopic constants of the low-lying bound states are in excellent agreement with measurements. Based on the accurately calculated structure parameters, the opacities of the oxygen molecule at the temperatures of 1000 K, 2000 K, 2500 K, and 5000 K under a pressure of 100 atm (1 atm=1.01325×10⁵ Pa) and the partition functions between 10 K and 10⁴ K are obtained. It is found that with the increase of temperature, the opacities for transitions in a long wavelength range are enlarged because of the larger population on excited electronic states at the higher temperatures.