Absolute differential and integral electron excitation cross sections for atomic nitrogen: 2. The 4So → 2p4 4P (λ1135 Å) transition from 30 to 100 eV

Abstract

The absolute direct differential and integral electron excitation cross sections for the atomic nitrogen 4So → 2p4 4P (λ1135 Å) transition have been measured at incident energies of 30, 50, and 100 eV. The differential cross sections measured versus scattering angle were integrated to give the integral cross section (ICS) as a function of incident energy. The ICS has a maximum value of 0.43×10−16 cm² (±30%) near 50 eV. Above 50 eV, the direct excitation cross section is within 20% of the fluorescence cross section of Stone and Zipf (1973) when the latter is adjusted downward to take account of the recent revision of the H2 dissociative excitation benchmark cross section. At 30 eV, the direct cross section is ∼1/10 of the fluorescence cross section. These results show that as for the λ1200‐Å N I transition cross section, there is a strong cascade contribution to the fluorescence cross section from forbidden transitions to higher states excited by low‐energy electron impact near threshold; but above 50 eV, unlike the λ1200‐Å N I transition cross section, there is only a small cascade contribution. The optical oscillator strength of the N I (λ1135 Å) multiplet obtained from the present data is 0.1 ± 0.005.