Proton Excitation of the Argon Atom

Studies of the excitation of argon with 4-MeV protons have been carried out by making use of a vacuum ultraviolet scanning monochromator and a 6-MeV Van de Graaff accelerator. Protons were directed through the gas and then into a Faraday cup in an arrangement in which the relative intensity of emitted light could be studied over a wide range of gas pressure (1 to 1500 Torr). Four continua near 2100, 1900, 1300, and 1100 \AA{}, respectively, as well as escape radiation originating from the 1048 \AA{} resonance line, were studied as a function of pressure.Studies of the intensity of the four main continua (per unit of proton power dissipation) as a function of pressure led us to the conclusion that each continuum has a separate atomic precursor. We suggest that the 1300 \AA{} continuum and the 1100 \AA{} continuum are dissociative diatomic continua and originate from the $^{1}P_{1}(11.83\ensuremath{-}\mathrm{e}\mathrm{V})$ and the $^{3}P_{1} (11.62\ensuremath{-}\mathrm{e}\mathrm{V})$ resonance atomic states, respectively. We tentatively suggest that the continua near 2100 \AA{} and near 1900 \AA{} are recombination spectra involving the formation of argon excimers with binding energies of about 4 eV.The 1300 and 1100 \AA{} continua have been observed in gas discharges, but these were interpreted as a single continuum originating from the $^{3}P_{1}$ state. We believe that the present experimental method, which makes possible gas kinetic observations at spectroscopically defined photon energies, is indeed a powerful tool for the study of atomic and molecular structure and processes.

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