N₂⁺ (X), N₂⁺ (A), and N₂⁺ (B) Production in e⁻ + N₂ collisions

Abstract

A variety of cross-section data for electron-impact ionization of N 2 have been analyzed, including those for total N•-production and for the Meinel and first-negative emissions from excited N•-ions. These results are used to infer the relative production rates of the N•-(X), N•-(A), and N•-(B) product ions during the reactions, yielding branching-ratio fractions of 0.320 _+ 0.147, 0.535 _+ 0.112, and 0.145 _+ 0.019, respectively, for 100-eV electrons. The data are compared with the relative formation rates of these ions recently obtained using electron-energy spectroscopy coincidence measurements. The significant discrepancy between these two procedures is discussed, and the results obtained from our data analysis are recommended for auroral modeling at the present time. N•-(X), N• (A), and N•-(B) states, respectively. This work was an extension of their earlier studies [Doering and Goembel, 1991] in which similar data were presented but for only a single secondary-electron emission angle. These initial results, (fx, f.4, fB) = (0.50, 0.40, 0.10), were compared favorably to the values (0.50, 0.39, 0.11) reported by Rees [1989] from an analysis of various ionization and emission cross-section data made by Lummerzheim [1987]. Unfortunately, the N•(A) data used for this analysis [Holland and Maier, 1972] were later found to be in error [Holland and Maier, 1973]. Using the "corrected" N•-(A) results, Crandall et al. [1974] subsequently estimated the branching ratios to be (0.25, 0.61, 0.14), now yielding a much smaller N•-(X) fraction than that found by Goembel et al. [1994]. In contrast, the (0.60, 0.25, 0.12) values of Nagata et al. [1987] suggest a larger fx branching ratio than found by Goembel et al. [1994], with an even larger fx being given by Kawazumi and Ogawa [1987]. Indeed, such scatter in the available branching-ratio data led Darrach and McConkey [1991] to adopt compromise values of (0.45, 0.45, 0.10) to minimize the disparities. The purpose of this paper is to analyze and evaluate the various ionization and emission cross-section data for electron impact on N 2 used in such branching-ratio determinations. We believe such an effort is justified, for the intense N•-Meinel and first-negative emissions observed during atmospheric aurorae or other airglow phenomena cannot be successfully modeled unless the N•-(A) and N•-(B) production rates are accurately known. Of course, the branching ratios found by Goembel et al. [1994] do not in themselves provide the cross-section magnitudes needed for such modeling work. Rather, they must be combined with an absolute value of the total N• production cross section to assess the contributions from these individual processes. For this reason we begin our study with the available data for total N•-formation. (Unless otherwise noted, the results discussed will be for 100-eV electron energy. This energy is at, or close to, the maxima of such cross sections and is the only energy investigated by Goembel et al. [1994] at this time.) We next consider the measured cross sectio...

Evaluation of electron impact excitation of N2 X 1Σg+(0) into the N2+ X 2Σg+(v), A 2Πu(v), and B 2Σu+(v) states

“…As a result, the sum of the cross sections for the production of the X 2 Σ g + , A 2 Π u and B 2 Σ u + states is often assumed to be the total cross section for nondissociative N 2 → N 2 + ionization. Van Zyl and Pendleton [1995] estimated a ∼2% contribution by the inner‐valence states to the total N 2 + production cross section at 100 eV electron impact energy. Because of the forbidden nature of the excitation to the higher states, the contribution of inner valance states is expected to decrease at higher energies.…”

“…The electron impact ionization cross sections of N 2 , dissociative and nondissociative, have been satisfactorily established as a result of many experimental investigations [ Rapp and Englander‐Golden , 1965; Schram et al , 1965; Crowe and McConkey , 1973; Märk , 1975; Krishnakumar and Srivastava , 1990; Freund et al , 1990; Straub et al , 1996; Tian and Vidal , 1998; Lindsay and Mangan , 2003]. However, the partial ionization‐excitation cross sections for the X 2 Σ g + , A 2 Π u , B 2 Σ u + states, assumed to be established earlier, were seriously questioned by Goembel et al [1994] and Doering and Yang [1996, 1997], and disputed in a thorough review by Van Zyl and Pendleton [1995]. Much of the dispute centers on the magnitude of the B 2 Σ u + state cross section, particularly at 100 eV.…”

“…Much of the dispute centers on the magnitude of the B 2 Σ u + state cross section, particularly at 100 eV. Van Zyl and Pendleton [1995], based on their analysis and the emission cross section measurement of Borst and Zipf [1970], suggested that the B 2 Σ u + state contributes 14.5% to the total N 2 + cross section. Goembel et al [1994] and Doering and Yang [1996, 1997] in electron scattering measurements, obtained much lower values of 9%–10%.…”

The 762 nm emissions of sprites

“…where N v′ is the population of the upper state vibrational level v′ in the band emissions, and A v′,v″ is the Einstein coefficient, which is the probability of radiative transition from the upper state vibrational level v′ to the lower state vibrational level v″ [Vallance-Jones, 1974]. In writing (1), it is assumed that the observed 1PN 2 emissions originate well above the quenching altitude of 53 km [Vallance-Jones, 1974], so collisional quenching is not important.…”

“…In writing (1), it is assumed that the observed 1PN 2 emissions originate well above the quenching altitude of 53 km [Vallance-Jones, 1974], so collisional quenching is not important. The population of the vibrational level v′, N v′ , is proportional to the Franck-Condon factor.…”