Hydrogen molecular effects on the Hα spectrum in low-temperature plasmas

The atoms dissociated from desorbed molecules occupy a large fraction of the neutrals in edge plasmas. Experiments of Palmer line emission, both in our linear devide MAP [1] and in TEXTOR [2], show a group of atoms at very low energy (< 1 eV). This paper evaluates the energy distributions of dissociated atoms of the most important reaction channels of H-2. It is shown that the vibrational excitation can lead to a broad range energy distribution for the Hz dissociated into ground state atoms. However, the contribution to the dissociated atoms at energies below 0.5 eV, is not so significant. The photon emission rate starting from H(2s) excitation is calculated and implemented in the DEGAS 2 modelling for our experiment case. From Ha modelling via DEGAS 2, it is concluded that the reaction channel, H-2+e --> H-2(1s sigma, nl lambda\(1)Lambda) --> e+H(1s)+H(2s), and especially one of the dissociated products H(2s) may be the main source contributing to the Balmer line emissions where the low-energy component was observed.