Molecular and atomic spectra emitted by normal liquid and supercritical 4He excited by corona discharge

Abstract

The properties of corona discharge were study by electro-physical and spectral methods in the supercritical phase at 6 K and 11 K as well as in normal liquid helium at 4.2K within the pressure range of 0.1-10 MPa. The electro-physical investigations (measurement of corona current as a function of the applied voltage) gave information about the mobility of charged particles in the medium. The observed corona current is very small, less than 10-7 A. The measured current-voltage characteristics allow for the calculation of the charged particle mobilities (i.e., electrons for negative corona and positive ions for positive corona). The observed charge mobilities decrease as a function of external pressure in both supercritical and liquid phases of helium. The light emitted from the ionization zone was analyzed and assigned to atomic and molecular lines. Distortion of the spectral lines due to the dense helium environment was analyzed. The observed P and R branch rotational line shifts of He2* are markedly different from the previous theoretical predictions. The observed atomic line shifts and widths depend strongly on the applied pressure in both the supercritical and the liquid phases, which can be understood in terms of a bubble formation around the emitters.