PROTON EXCITATION OF 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, respectively, as well as escape radiation originating from the 1048 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 continuum and the 1100 continuum are dissociative diatomic continua and originate from the P11 (11.83-eV) and the P13 (11.62-eV) resonance atomic states, respectively. We tentatively suggest that the continua near 2100 and near 1900 are recombination spectra involving the formation of argon excimers with binding energies of about 4 eV. The 1300 and 1100 continua have been observed in gas discharges, but these were interpreted as a single continuum originating from the P13 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. © 1969 The American Physical Society.