Resonance scattering of positronium atoms by nitrogen molecules

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We study theoretically the resonance scattering of positronium (Ps) atoms by nitrogen molecules and compare it with resonance e–N2 scattering in the Πg symmetry. The velocity positions of the Ps–N2 resonances in Σu, Πu, and Δg symmetries are very close to the velocity position of the e–N2 resonance which leads to the total Ps–N2 cross section being very similar to the e–N2 cross section when both are plotted as functions of the projectile velocity. However, in the Ps–N2 case the resonances are much wider and their positions vary much slower with increasing internuclear separation than in the e–N2 case. This makes the Ps-impact vibrational excitation cross section much smaller than the electron-impact vibrational excitation cross section, and no boomerang oscillations are observed in Ps–N2 scattering. We analyze the role of the static potential in the e–N2 case and compare exchange potentials for e–N2 and Ps–N2 interactions. This analysis allows us to explain the difference in the vibrational dynamics in these two cases.