Collisional removal of O2(b 1Σg+,υ=2,3)

The temperature dependence of the collisional removal of O2 in the υ=3 level of the b 1Σg+ state by N2, O2, and CO2 was investigated at room temperature and below. Measurements on the υ=2 level with the colliders, O2, N2O, Ar, and He are also reported. For υ=3 removal by O2, the trend of sharply decreasing loss rate coefficients with increasing υ is seen to continue. For example, at 200 K the rate coefficient for collisional removal of O2 from the υ=3 level by O2 is some three orders of magnitude smaller than that for the υ=1 level. We argue that the mechanism of the deactivation is electronic–electronic (E–E) energy transfer. Observation of emission from a broad range of O2(b 1Σg+) vibrational levels in the terrestrial nightglow, recently discovered in astronomical sky spectra, show less than an order of magnitude difference in population between the more highly populated υ=3 level and the less populated υ=1 level. The implications of these two observations on the vibrational-level-specific atmospheric sources of vibrationally excited molecules in the b 1Σg+ electronic state are explored.