Measured densities and rotational temperatures of metastableH2in a multicusp ion source

Abstract

We report the first successful application of resonant multiphoton ionization to the diagnosis of a discharge. This technique is used to measure rotational temperatures of ${\mathrm{H}}_2$ in the metastable c ${\mathrm{}}^3$ ${\mathrm{\Pi }}_{\mathrm{u}}^{\mathrm{-}}$ state, which are in the range of 400 to 600 K. The density of these molecules is determined by a single-photon ionization process, yielding a value of 3×${10}^9$ ${\mathrm{cm}}^{\mathrm{-}3}$ at a discharge current of 30 A. The relevance of these metastable molecules to ${\mathrm{H}}^{\mathrm{-}}$ production in hydrogen discharges is discussed.