Absolute Cross Sections for Excitation of Nitrogen by Protons of a Few kev Energy

Abstract

Cross sections for excitation by proton impact are necessary for quantitative interpretation of auroral spectra. These have been measured for excitation resulting when protons of a few kev energy shoot into low-pressure nitrogen. Interference filters select various spectral features and a photomultiplier detects the light emitted. The light-detection apparatus is calibrated against a standard tungsten filament lamp. The measured cross sections are not for the excitation of a given molecular level, but for a process resulting in the emission of one photon in a given transition. Cross sections measured include: the 0,0 first negative band of ${\mathrm{N}}_2^{+}$, $\lambda 3912$; the 2,0 Meinel band of ${\mathrm{N}}_2^{+}$, $\lambda 7850$; a group of N i lines around $\lambda 8216$; the Balmer line ${\mathrm{H}}_{\beta }$; and the (4,2) and (3,1) first positive bands of ${\mathrm{N}}_2$, excited by impact of fast atoms. Results are presented graphically, covering the range 1.5 to 4.5 kev. Also included are measurements of the total charge-exchange cross section for protons in nitrogen and an estimate of the ionization cross section.