Spectra, line intensities of the C1Σg+ ⇒ A1Σu+ and c3Σg+ ⇒ a3Σu+ transitions in liquid normal He, and rotational level populations of the C1Σg+ and c3Σg+ the terms

Abstract

We observed the rotational spectral lines of the He*₂ excimer within the range of 910–930 nm in the corona discharge in normal liquid He at the temperature of 4.2 K and the pressure of 1 atm. The spectral range is filled with the rotational lines of the C¹Σ_g⁺ ⇒ A¹Σ_u⁺ singlet and the c³Σ_g⁺ ⇒ a³Σ_u⁺ triplet transitions. These transitions end at the rotational levels of the lowest metastable terms, A¹Σ_u⁺ and a³Σ_u⁺ of the He*₂ excimer. Then, the population of the rotational levels with the K' number of the upper C¹Σ_g⁺ and c³Σ_g⁺ terms (the quantity of the molecules with the rotational moment of K' in the excited molecule ensemble in the discharge) is proportional to the intensity of the rotational lines marked K' of the C¹Σ_g⁺ ⇒ A¹Σ_u⁺ singlet and the c³Σ_g⁺ ⇒ a³Σ_u⁺ triplet. The populations might be calculated according to the experimental intensities of the rotational spectral lines. The emitting corona plasma in the liquid He is nonequilibrium and the rotational level populations do not correspond to the Boltzmann distribution. The efficient rotational temperature exceeds the liquid He temperature, 4.2 K.