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Languages : en
Pages : 280
Book Description
Low pressure H2 discharges have been used for some time as sources of H− ions. These discharges contain many different species of particles which interact with each other and with the walls of the discharge chamber. Models exist that predict the populations of the various species for given macroscopic discharge parameters. However, many of the cross sections and wall catalyzation coefficients are unknown or somewhat uncertain. Therefore, it is of interest to measure the populations of as many of these species as possible, in order to determine the validity of the models. These models predict that H− is created predominantly by the two-step process of vibrational excitation of hydrogen molecules followed by dissociative attachment of slow electrons to these vibrationally-excited hydrogen molecules. Many different collisional processes must be included in the models to explain the dependence of the various populations upon macroscopic parameters. This work presents results of spectroscopic measurements of the density and translational temperature of hydrogen atoms and of specific rotationally- and vibrationally-excited states of electronic ground-state H2, in a discharge optimized for H− production, as well as conventional measurements of the various charged species within the plasma. The spectroscopic measurements are performed directly by narrowband, single-photon absorption in the vacuum ultraviolet.
