# Article

Plasma Investigations

2017. V. 55. № 2. P. 165–173

Atrazhev V.M., Shakhatov V.A., Boltnev R.E., Bonifaci N., Aitken F., Eloranta J.

Spectra, line intensities of the $C^1\Sigma_g^+ \rightarrow A^1\Sigma_u^+$ and the $c^3\Sigma_g^+ \rightarrow\,a^3\Sigma_u^+$ transitions in liquid normal $\rm He$, and rotational level populations of the $C^1\Sigma_u^+$ and the $c^3\Sigma_u^+$ terms

We observed the rotational spectral lines of the excimer within the range of $910$–$930$ nm in the corona discharge in normal liquid $\rm He$ at the temperature of $4.2$ K and the pressure of $1$ atm. The spectral range is filled with the rotational lines of the $C^1\Sigma_g^+ \rightarrow A^1\Sigma_u^+$ singlet and the $c^3\Sigma_g^+ \rightarrow a^3\Sigma_u^+$ triplet transitions. These transitions end at the rotational levels of the lowest metastable terms, $A^1\Sigma_u^+$ и $a^3\Sigma_u^+$ and of the excimer. Then, the population of the rotational levels with the $K'$ number of the upper $C^1\Sigma_u^+$ and $c^3\Sigma_u^+$ 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 $C^1\Sigma_g^+ \rightarrow A^1\Sigma_u^+$ singlet and the $c^3\Sigma_g^+ \rightarrow a^3\Sigma_u^+$ triplet. The populations might be calculated according to the experimental intensities of the rotational spectral lines. The emitting corona plasma in the liquid $\rm He$ is nonequilibrium and the rotational level populations do not correspond to the Boltzmann distribution. The efficient rotational temperature exceeds the liquid $\rm He$ temperature, $4.2$ K.

Article reference:

*Atrazhev V.M., Shakhatov V.A., Boltnev R.E., Bonifaci N., Aitken F., Eloranta J.*Spectra, line intensities of the $C^1\Sigma_g^+ \rightarrow A^1\Sigma_u^+$ and the $c^3\Sigma_g^+ \rightarrow\,a^3\Sigma_u^+$ transitions in liquid normal $\rm He$, and rotational level populations of the $C^1\Sigma_u^+$ and the $c^3\Sigma_u^+$ terms, High Temp., 2017. V. 55. № 2. P. 165