Positron impact electronic excitation of N2

We present the results of scattering cross sections for positron impact excitation of electronic states of nitrogen molecule (N-2) using the Schwinger multichannel method (SMC). All calculated cross sections took three collision channels into account (X(1)Sigma(g) and degenerate a(1)Pi(g), states). Present theoretical results for excitation to the a(1)Pi(g). states failed to reproduce the near-threshold structure observed in the recent and the only available experimental data [Sullivan et al., Phys. Rev. Lett. 87 (2001) 073201-1]. Scattering calculations from the a(1)Pi(g), states (elastic and superelastic) are also reported. A spurious resonant structure found in the excitation to the a(1)Pi(g) states was detected in a square integrable basis set calculation designed to reproduce the first Born approximation (FBA). Such spurious structure was removed by taking out the trial configuration state functions in which the positron was weakly coupled to the target. This may be a promising technique to separate unphysical resonances from the physical ones. We also observe that a combination between SMC scattering amplitudes (I less than or equal to, 2) with FBA ones (1 greater than or equal to 3) significantly improved the cross sections at higher energies. (C) 2004 Elsevier B.V. All rights reserved.