Intensity Enhancement of Weak O2 a1Δg → X3Σg– Emission at 1270 nm by Collisions with Foreign Gases

Collision-induced near-IR emission of O(2) a(1)Δ(g) was investigated in O(2)/M (M = Ar, Kr, Xe, N(2), or CO(2)) gas mixtures, where the total pressure ranged from 10 to 100 atm, and gaseous O(2) dimol was excited with a pulsed dye laser at 630 nm through the simultaneous two-electron transition to prepare O(2) in the a(1)Δ(g) state. The a(1)Δ(g) → X(3)Σ(g)(-) emission intensity around 1270 nm increased with the number density of foreign gas (M) under constant O(2) number density. Emission enhancement efficiencies were in the order Xe > CO(2) > O(2) > Kr > N(2) > Ar; they are controlled by collisional enhancement during the near-IR emission at 1270 nm but not during photoabsorption at 630 nm. Efficiencies were converted into bimolecular rate constants to enhance the radiative a → X transition for the added gases. The rate constants were estimated as quadratically dependent on the molar refraction (or polarizability) of collision gas. The self-quenching rate constant was determined from the Stern-Volmer plot of the emission lifetimes measured in pure O(2).