The kinetics of H- ion formation in hydrogen plasmas studied using vacuum ultraviolet laser absorption spectroscopy

Vacuum ultraviolet laser absorption spectroscopy has been used to measure the atomic and molecular hydrogen populations present in medium power, medium density (5KW, 1012 electrons -cm-3) hydrogen plasmas. Translation temperatures of the ground electronic state atoms and molecules are obtained, with the rotational-vibrational state distributions of the molecules also being determined. Vibrational levels up to v=8 have been observed. This is the first time these highly vibrationally-excited levels been observed in situ in a plasma. The plasmas studied are typical of those used for production of H- ions. The currently accepted models of these systems show a strong dependence of the H- production with the H and H2 populations. The proposed mechanism of H- formation is evaluated in light of the new experimental measurements