Laboratory studies of UV emissions from proton impact on N₂: The Lyman-Birge-Hopfield band system for aurora analysis

Abstract

[1] We have measured the emission cross sections of the Lyman-Birge-Hopfield (LBH) a 1 P g − X 1 S g + band system and several atomic nitrogen (N I) multiplets (1200, 1243, 1493 Å) by H + (proton) impact on N 2 over an impact energy range of 1-7 keV. The peak proton-impact-induced emission cross section of the LBH band system (1260-2500 Å) was measured to be 5.05 ± 1.52 × 10 −17 cm 2 at 7 keV. To the best of our knowledge, the present LBH emission cross sections are reported for the first time in the far ultraviolet (FUV) wavelength range of 1100-1600 Å. The proton energy range in this study, when coupled with previously published 10-100 keV proton excited emissions of N I multiplets, provides a wide energy range of emission cross sections for proton energy loss transport codes. This energy range includes the peak cross section and the energy range for Born scaling. The reported measurements lead to an important component of monoenergetic yields for proton FUV auroral emission. Such yields, based on emission cross sections and transport modeling, allowed for convenient comparison of emission efficiencies between proton and electron aurora. In addition, we have measured the H Ly a, LBH, and N I multiplet emission cross sections for H 2 + and H 3 + ion impact on N 2 at 5 keV and found that the magnitude of H Ly a emission cross section, s em (Ly a), follows in the order of impact ion mass H 3 + > H 2 + > H + .Citation: Ajello, J. M., R. S. Mangina, D. J. Strickland, and D. Dziczek (2011), Laboratory studies of UV emissions from proton impact on N 2 : The Lyman-Birge-Hopfield band system for aurora analysis,

THE HIGH-RESOLUTION EXTREME-ULTRAVIOLET SPECTRUM OF N 2 BY ELECTRON IMPACT

“…(Ajello et al 2007;James et al 1990). For sufficiently energetic electron or proton collisions, a comparable amount of emission arises from the decay of excited atomic dissociation products (Ajello & Shemansky 1985;Ajello et al 1989Ajello et al , 2011aAjello et al , 2011b. Further electron-induced fluorescence occurs from the Lyman-Birge-Hopfield (LBH) series of bands originating from the a 1 Π g excited state.…”

“…The UV emission studies of N 2 by electron-impact-induced fluorescence carried out over the past 30 years at the Jet Propulsion Laboratory (JPL) have been motivated by both astrophysical and theoretical interest (Ajello & Shemansky 1985;Ajello et al 1989Ajello et al , 1998Ajello et al , 2007Ajello et al , 2008Ajello et al , 2011aAjello et al , 2011bAjello et al , 2012James et al 1990;Mangina et al 2011;Young et al 2010). Intense atomic emissions in the dayglow from the atmospheres of N 2 -bearing solar system objects occur mainly from solar photodissociative ionization (PDI) and in the nightglow by collision with secondary electrons and other particles (e.g., magnetospheric protons and O + ; Ajello et al 2011aAjello et al , 2011bAjello et al , 2012Cravens et al 2008Cravens et al , 2010. The LBH molecular bands, the strongest band system in the far ultraviolet (FUV; 1200-2500 Å), excited by particle impact appear strongly in planetary atmospheres containing N 2 as a major species (Ajello et al 2011a).…”

“…The important electronic transitions proceed from the X 1 Σ g + ground state to a manifold of closely spaced (12-15 eV) states (Ajello et al 2011b), which are then the sources of EUV emissions observed by spacecraft (Ajello et al 2007(Ajello et al , 2011aStevens et al 2011). Two of these states, b 1 Π u and b 1 Σ u + , are of the valence type and the remainder fall into three Rydberg series, with lowest members c 4 1 Σ u + , c 3 1 Π u , and o 3 1 Π u .…”

“…Intense atomic emissions in the dayglow from the atmospheres of N 2 -bearing solar system objects occur mainly from solar photodissociative ionization (PDI) and in the nightglow by collision with secondary electrons and other particles (e.g., magnetospheric protons and O + ; Ajello et al 2011aAjello et al , 2011bAjello et al , 2012Cravens et al 2008Cravens et al , 2010. The LBH molecular bands, the strongest band system in the far ultraviolet (FUV; 1200-2500 Å), excited by particle impact appear strongly in planetary atmospheres containing N 2 as a major species (Ajello et al 2011a). The particle-impact fluorescence of the ensemble of Rydberg and valence bands of N 2 studied in this paper are all of importance in planetary observations (Avakyan et al 1998;Stevens et al 2011;Lavvas et al 2011) but have never been comprehensively studied in the EUV at high resolution.…”

Ab initiocalculation of charge transfer in proton collisions with N2

“…One of the important processes that take place in these events is charge transfer (CT), which leads to the ionization of the molecules and the possible production of fast neutrals. In this paper we concentrate on the study of proton collisions with nitrogen molecules, events that can occur in the polar regions of the Earth's atmosphere [8,9] due to the incoming flux of the solar wind, in which the typical energies of the protons are of the order of a few keV [10,11]. Proton collisions with N 2 may also be relevant in the edge of tokamak plasmas if N 2 is used as a scavenger, as suggested in Ref.…”