Formation of H− ions via vibrational excited molecules produced from recombinative wall desorption of H atoms in a low-pressure H2 positive column

Recombinative wall desorption of hydrogen atoms in a low-pressure hydrogen positive column leading to formation of H2 (X1Σ+g, v) molecules in optimum levels for H− production by dissociative attachment is investigated. We employed a kinetic model that solves the Boltzmann equations for electrons, coupled to a set of rate balance equations for vibrational levels H2 (X1Σ+g, v), dissociated atoms H(1s) and negative ions H−. It is shown that the relative concentration [H−]/[H2] is two times greater when recombinative wall desorption of H atoms is included in the model, for discharge pressures in the range p=0.03–1.0 Torr and currents of 5 and 20 mA.