Excitation of the O2(a 1Δg) state by low energy electrons in O2–N2 mixtures

Abstract

Coefficients for the excitation of the a 1Δg state of O2 by low energy electrons in mixtures of O2–N2–Ar and O2–N2 and in pure O2 have been determined using a drift tube technique. The time dependence of the absolute intensity of 1.27 μm band emission was measured for 1% to 5% O2 and 1% to 10% N2 in Ar at total gas densities of 2 to 10×1024 m−3 and in 20% O2–80% N2 mixtures at a total density of about 2×1024 m−3. The measured decay constants for O2(a 1Δ) metastable densities in these mixtures are in agreement with previous data. Comparison of experimental and calculated excitation coefficients for the mixtures shows the importance of a 1Δg excitation by cascading from the states of the A 3Σ+u, C 3Δu, and c 1Σ−u group near 5 eV in O2 for mean electron energies between 1.5 and 5 eV. Using published a 1Δ deexcitation rate coefficients, the measurements of absolute intensity at 1.27 μm from pure O2 yield excitation coefficients that agree satisfactorily with theory at E/N values of 8–20×10−21 Vm2.