Optical absorption spectra and kinetic behavior of helium excited diatomic molecule (<i>a</i> 3Σ<i>u</i>+)

Abstract

The transient absorption spectra of electron-irradiated 12-atm helium have been measured in the wavelength region 3000–11 000 Å. The observed molecular absorptions correspond to the c 3Σg+←a 3Σu+, e 3Πg←a 3Σu+, and i 3Πg←a 3Σu+ transitions, short-lived atomic absorptions arising from He*(23S) being observed at several wavelengths. The rotational temperature of He*2(a 3Σ+u, v″=0) produced initially is estimated to be room temperature from the intensity distribution of the P branch. The vibrational deactivation rate of He*2(a 3Σu+, v″=1) depends linearly on helium pressure, the rate constant being 1.0×10−14 cm3 sec−1. The rate constants of the quenching reactions of He*2(a 3Σu+, v″=0) by Ne, Ar, Kr, Xe, H2, N2, O2, CO, NO, N2O, and CO2 have been determined from time-dependent measurements of the absorption decay. The rate constants range from 0.4×10−10 cm3 sec−1 for Ne to 1.0×10−9 cm3 sec−1 for CO2. An intense emission and absorption were observed at 7772 Å in the quenching processes of He*2(a 3Σu+, v″=0) by oxygen-containing compounds.