Magnetic phosphorescence of molecular oxygen. A study of the b ¹∑⁺_g-x ³∑^-_g transition probability using multiconfiguration response theory

Multiconfigurational response function calculations of the magnetic dipole transition moment for the red atmospheric emission band b ¹∑⁺_g-X ³∑^-_g in O₂ have been performed at different internuclear distances. Spin and orbital angular momentum contributions are calculated as residues of the linear and quadratic response functions using the full Breit-Pauli spin-orbit coupling operator. Vibronic band intensities are calculated by vibrational averaging of the magnetic dipole transition moments and compared with experimental data. The Einstein coefficient for the 0,0 transition probability (0.079 s^-1) is obtained 10% smaller than the most recent experimental result of Ritter and Wilkerson (0.089 s^-1), but in fair agreement with previous experimental data (0.077-0.0825 s^-1), while an excellent agreement for all other known vibronic transition probabilities for the red atmospheric band is obtained.