Benchmarking electronic-state excitation cross sections for electron-N2 collisions

We report differential cross sections for electron impact excitation of the a 1Πg, C 3Πu, E 3Σg+, a''1Σg+, b 1Πu, c31Πu, o31Πu, b'1Σu+, c4'1Σu+, G 3Πu, and F 3Πu electronic states in N2. The incident electron energies are 20, 30, and 40 eV, while the scattered electron angles are 10 deg. and 20 deg. These kinematic conditions were specifically targeted in order to try and shed new light on the worrying discrepancies that exist in the literature for the a 1Πg, C 3Πu, E 3Σg+, and a''1Σg+ cross sections, and in general the present measurements confirm that those from the more recent results of the University of California, Fullerton, and the Jet Propulsion Laboratory [M. A. Khakoo, P. V. Johnson, I. Ozkay, P. Yan, S. Trajmar, and I. Kanik, Phys. Rev. A 71, 062703 (2005); C. P. Malone, P. V. Johnson, I. Kanik, B. Ajdari, and M. A. Khakoo, Phys. Rev. A 79, 032704 (2009)] are reliable. In addition, we provide a rigorous cross-check for the remaining seven electronic states, where the only recent comprehensive study is from Khakoo and colleagues [Phys. Rev. A 77, 012704 (2008)]. Here, however, some of those cross sections are confirmed and others are not, suggesting that further work is still needed.