Electron energy dependence of vacuum ultraviolet emission and H− production in a low-pressure hydrogen plasma

A two-step process of pure H- volume production via vibrationally excited ground state molecules H2(v5) is discussed. The principal source of this vibrational excitation is through singlet excitation by fast primary electrons followed by vacuum ultraviolet (VUV) emission. The VUV emission from a low-pressure hydrogen plasma has been used to study the production mechanism of H2(v5) molecules and its electron energy dependence, in a double plasma source where both energy and density of fast electrons are well controlled. The fast electron energy and density strongly affect the VUV emission intensity at wave lengths of, for example, 123 and 124.9 nm. There exists a certain threshold in fast electron energy for singlet excitation and then for H2(v) excitation. Fast electrons with energy in excess of 15-20 eV mainly contribute to the VUV emission intensity and are sufficient to increase H- production