HIGH-RESOLUTION STUDIES OF DIPOLE-FORBIDDEN STATES OF N-2 USING LOW-ENERGY ELECTRON ENERGY-LOSS SPECTROSCOPY

Energy-loss spectra for molecular nitrogen have been measured with impact energies between 0.5 and 100 eV above the threshold for excitation and at scattering angles between 2 and 60 degrees . The energy-loss range between 5 and 25 eV was studied, with a typical resolution of approximately 0.025 eV. At energy losses below 11 eV the observed spectra can be fully assigned, with the exception of one progression of very weak peaks, using dipole-forbidden states previously observed in emission studies. The angular distribution of one of these states, w1 Delta u was measured. Between 14.30 and 15.90 eV, six energy-loss peaks were found to have angular distributions typical of dipole-forbidden transitions which cannot be related to previously observed states of N2. Above the ionisation limit, three new Rydberg series of states converging to the nu =0 level of the B2 Sigma u+ state of N2+ were detected at high scattering angles and low impact energies.