Excitation of the O2(a 1Δg) state by low energy electrons

Coefficients for the excitation of the a 1Δg metastable state of O2 by low energy electrons in O2–Ar mixtures have been measured using a drift tube technique. The time dependence of the absolute intensity of the 1.27 μm band emission was measured for 1% and 5% O2 in Ar at total gas densities of (1–20)×1024 m−3. The electric field to gas density ratio E/N was varied from (0.3–10)×10−21 V m2, corresponding to calculated mean electron energies between about 0.8 and 4 eV. The measured decay constants yield a normalized diffusion coefficient for O2(a 1Δg) in Ar of (2.8±0.2)×1020 m−1 s−1 and a rate coefficient for quenching by O2 of (1.57±0.1)×10−24 m3 s−1. Our experimental electron excitation coefficients agree satisfactorily with values calculated using previously derived sets of electron collision cross sections for O2 and Ar.