Nonmonotonic distribution of population of the a3Σu+ triplet state rotational levels in corona discharge in cryogenic helium gas

Abstract

We observed the spectra within the wavelength range of 910–990 nm of emission of the corona discharge in supercritical helium gas at 6–11 K. This spectral range contains the molecular bands of the He*₂ excimer radiative transitions (c³Σ_g⁺ ⇒ a³Σ_u⁺) between the electron-vibrational-rotational levels of the c³Σ_g⁺ and the a³Σ_u⁺ triplet states. We have determined the populations of the rotational levels (quantity of molecules in the given excited state among the excited molecules of the discharge) of the c³Σ_g⁺ excited state from experimental values of the intensity of the respective electron-vibrational-rotational lines. The calculated population distribution is nonmonotonous. The population of the level with the rotation quantum number K′ = 18 (the level number) is higher than those of the levels with the other K′ values.