ROTATIONAL AND VIBRATIONAL-EXCITATION OF NITROGEN BY ELECTRON-IMPACT

Rotational excitation of nitrogen by low-energy electron impact has po sed an unsolved problem for more than three decades. Early analysis of the results of swarm experiments in nitrogen found that the data coul d be matched remarkably well by assuming that the energy dependences o f the Delta j = 2 cross sections from threshold to a few tenths of an eV are given by a simple formula based on the Born approximation. More over, the quadrupole moment (the only adjustable parameter in the form ula) which gave the best fit to the data was commensurate with existin g experimental values. This finding posed an enigma, since the quadrup ole Born expression is known to incorrectly represent the interaction potential for scattering except within a few meV of threshold. We have analysed new swarm data, taken in a dilute mixture of nitrogen in neo n, using theoretical rotational and momentum transfer cross sections b ased on a solution of the Schrodinger equation using static, exchange, and polarisation potentials. This work explains the long-standing eni gma and provides the basis for a subsequent analysis in which theoreti cal vibrational excitation cross sections are also investigated using the new swarm data for the mixture.