Rotational excitation of nitrogen by low-energy electron impact has posed an
unsolved problem for more than three decades. Early analysis of the results of
swarm experiments in nitrogen found that the data could be matched remarkably
well by assuming that the energy dependences of the
Δj = 2 cross sections from threshold to a
few tenths of an eV are given by a simple formula based on the Born
approximation. Moreover, the quadrupole moment (the only adjustable parameter
in the formula) which gave the best fit to the data was commensurate with
existing experimental values. This finding posed an enigma, since the
quadrupole 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 mixure of nitrogen in neon, using
theoretical rotational and momentum transfer cross sections based on a
solution of the Schrödinger equation using static, exchange, and
polarisation potentials. This work explains the long-standing enigma and
provides the basis for a subsequent analysis in which theoretical vibrational
excitation cross sections are also investigated using the new swarm data for
the mixture.
Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2and NO molecules
