Oxygen nightglow emissions of Venus: Vertical distribution and collisional quenching

We compare the altitude of three O2 night airglow emissions observed at the limb of Venus by the VIRTIS spectral imager with those values predicted by a model accounting for the different radiative lifetimes and collisional deactivation of the upper O2 states. The O and CO2 density profiles are based on remote sensing observations from the Venus Express spacecraft. Effective production efficiencies of the involved O2 metastable states and quenching coefficients by oxygen and carbon dioxide are adjusted to provide the best match with the measured emission limb profiles. We find values in general good agreement with earlier studies for the c 1 Σ u - state which gives rise to the Herzberg II bands. In particular, we confirm the low net yield of the c state production and the importance of its deactivation by CO2, for which we derive a quenching coefficient of 3 × 10−16 cm−3 s−1. The ∼4.5 km higher altitude of the Chamberlain band emission also recently detected by VIRTIS and the ratio of the Herzberg II/Chamberlain bands observed with Venera are well reproduced. To reach agreement, we use a 12% yield for the A′3Δu production following O atom association and quenching coefficients by O and CO2 of 1.3 × 10−11 cm−3 s−1 and 4.5 × 10−13 cm−3 s−1 respectively. We conclude that the different peak altitudes of the IR Atmospheric, Herzberg II and the Chamberlain bands reflect the relative importance of radiative relaxation and collisional quenching by O and CO2.