Fluorescence Spectra of the Excited Ion N2+ Resulting from Vaccum-Ultraviolet Photon Impact on N2

Abstract

The spectrum of the radiation between 3500 and 6500 Å, resulting from the impact of monochromatic vacuum-ultraviolet radiation on N2, is obtained for incident-photon energies between 18.8 (661 Å) and 26.8 eV (460 Å), and the vibrational progressions and sequences of the first negative system of nitrogen, N2+(B 2Σu+→X 2Σg+) are identified. For incident photon energies less than 18.8 eV no significant radiation was observed. From an intensity measurement of the bands of the first negative system, experimental Franck–Condon factors for the transitions N2[X 1Σg+(υ″ = 0)]→N2+[B 2Σu+(υ′ = 0, 1)] and N2+[B 2Σu+(υ′ = 0, 1)]→N2+[X 2Σg+(υ″ = 0, 1, 2)] were obtained and found to agree reasonably well with theoretical values, calculated using Morse potentials. In addition, the absolute ionization cross section vs incident photon energy for the ionic state N2+[B 2Σu+(υ′ = 0)] is presented for the above indicated range of incident photon energies. The lower energy of 18.8 eV is the threshold energy for excitation to this ionic state. An observed quenching at N2 pressures above 100 μ may arise from excitation transfer in ion–molecule reactions, although no spectral changes were observed as a function of gas pressure.