Studies on the production of O 2 ( a 1 Δ g , υ = 0) and O 2 ( b 1 Σ g + , υ = 0) from collisional removal of O 2 ( A 3 Σ u + , υ ′ = 6–10)

Production of two metastable O 2 species, O 2 ( a 1 Δ g , υ = 0) and O 2 ( b 1 Σ g + , υ = 0), from collisional removal of O 2 ( A 3 Σ u + ) by O 2 and N 2 is investigated at a temperature of 240 K. A state‐selective two‐laser technique is used, in which the output of the first laser excites ground‐state O 2 molecules to a specific vibrational level (6 ≤ υ ′ ≤ 10) in the A 3 Σ u + state, and the output of the second laser subsequently probes the O 2 ( a 1 Δ g , υ = 0) and O 2 ( b 1 Σ g + , υ = 0) populations by resonance‐enhanced multiphoton ionization via the intermediate d 1 Π g Rydberg state. For the relatively short timescales of our experiment (∼10 −4 Torr·s), we find that the O 2 ( a 1 Δ g , υ = 0) quantum yield from collisional removal of O 2 ( A 3 Σ u + , υ ′) by O 2 is approximately constant for υ ′ = 7–9, and decreases by 30–40% for υ ′ = 6 and 10. The O 2 ( b 1 Σ g + , υ = 0) yield is nearly constant for υ ′ = 8–10, and decreases by about 50% for υ ′ = 6 and 7. The eventual O 2 ( a 1 Δ g , υ = 0) and O 2 ( b 1 Σ g + , υ = 0) yields from O 2 ( A 3 Σ u + , υ ′ = 8) measured in synthetic air are nearly equal to those measured in pure O 2 , suggesting that N 2 collider does not significantly affect the relaxation pathways leading to the production of the two metastable species. However, at short experimental times the buildup of the O 2 ( a 1 Δ g , υ = 0) population is considerably slower in synthetic air than in O 2 .