Production of Light by Collisions of 2.5–490 eV He+ with N2: NI, N2+ Second Negative, and Unresolved Emissions between 1200 and 3200 Å

Abstract

The production of light in collisions between He⁺ and N₂ has been studied at primary ion energies, $E$ , between 2.5 and 490 eV. Strong emissions are present between 1200 and 3200 Å, and spectra have been obtained for spectral resolutions between 1.5 and 16 Å. NI emissions, N₂⁺ second negative $\text{(2N)}$ emissions, and strong, unresolved emissions have been found. The total cross section for producing the emission between 1200 and 3200 Å is of the order of 10⁻¹⁶ cm². For $\text{E\hspace{0.17em}<̃\hspace{0.17em}40}\mathrm{eV}$ , the cross section for producing the unresolved emissions is greater than the cross section for producing the ${\mathrm{N}}_2^{+}\text{(2N)}$ emissions. The cross section for production of the NI emissions decreases with decreasing $E$ and vanishes near the threshold energies expected for NI emission produced by He⁺+N₂→N⁺+N+He. With decreasing $E$ , total cross sections for the ${\mathrm{N}}_2^{+}\text{(2N)}$ and unresolved emissions increase. Apparent populations of the vibrational levels of the ${\mathrm{N}}_2^{+}\text{(2N)}$ parent state depend differently on $E$ ; in particular, for $\text{E\hspace{0.17em}=\hspace{0.17em}490}\mathrm{eV}$ the $\text{υ′\hspace{0.17em}=\hspace{0.17em}1}\mathrm{and}2$ levels are the most highly populated, and for $\text{E\hspace{0.17em}=\hspace{0.17em}4.5}\mathrm{eV}$ the $\text{υ′\hspace{0.17em}=\hspace{0.17em}3}\mathrm{and}4$ levels are the most highly populated. The electronic transition moment of the $C^2{\Sigma }_u^{+}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}X}}^2{\Sigma }_g^{+}$ transitions, which produce the $N_2^{+}\text{(2N)}$ emissions, varies considerably with the wavelength of the emitted light.