Collisional removal of O2(b1Σg+, υ = 1) by O2 at thermospheric temperatures

Collisional removal of O2(b1Σg+, υ = 1) by O2 is investigated at temperatures relevant to the lower thermosphere. A two‐laser technique is used, in which the visible output of the first laser directly excites ground‐state oxygen molecules to the υ = 1 level of the b1Σg+ state and the ultraviolet output of the second laser probes the O2(b1Σg+, υ = 1) population by resonantly enhanced multiphoton ionization via the υ = 4 level of the d1Πg Rydberg state. The collisional removal rate coefficient increases with temperature by a factor of five in the range 300–1000 K, with a value of about 8 × 10−11 cm3 s−1 near 1000 K. Given the magnitude of the rate coefficient, the removal by O2 plays a dominant role in controlling the population of O2(b1Σg+, υ = 1) in the mesosphere and lower thermosphere at altitudes below 150 km and likely continues to be an important removal pathway at altitudes up to about 200 km.