Excitation of the Herzberg bands of O₂in laboratory afterglow and night airglow

Relative vibrational populations of the metastable O2 A³Σu+ molecule were calculated from a statistical equilibrium model and compared with vibrational populations determined spectroscopically in an oxygen-argon afterglow at pressures of 5–120 torrs and with the nightglow populations obtained previously. The model assumes the three-body recombination process to be the principal excitation mechanism and vibrational relaxation to be the principal collisional deactivation mechanism. A close fit is obtained with both sets of data when the excited molecule is treated as an anharmonic oscillator during the relaxation process ; thus the peculiar distributions of band intensities observed in the Herzberg band spectra (A³Σu+ − X³Σg−) are the consequence of the strongly anharmonic character of the O2A³Σu+ molecule rather than of some other processes. Although the formulation provides for collisional quenching, the data are not as yet sufficiently complete to make a firm estimate.