Cross section forelectron-impact excitation of the /0,0/ first negative band of N2/plus/ from threshold to 3 kev
TL;DR: In this paper, the first negative band of nitrogen ion from threshold to 3 keV was measured using photon counting techniques. But the authors did not consider the negative band in this work.
Abstract: Electron impact excitation cross section of /0,0/ first negative band of nitrogen ion from threshold to 3 keV, using photon counting techniques
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TL;DR: A review of the field of airglow analysis can be found in this article, where the basic processes leading to excitation of atomic and molecular energy states are discussed and the current status of knowledge of individual emission features seen in the air glow is examined for the purpose of selecting those species most useful as diagnostics of the state of the upper atmosphere and ionosphere.
Abstract: The Earth's ultraviolet airglow contains fundamental diagnostic information about the state of its upper atmosphere and ionosphere. Our understanding of the excitation and emission processes which are responsible for the airglow has undergone dramatic evolution from the earliest days of space research through the past several years during which a wealth of new information has been published from high-resolution spectroscopy and imaging experiments. This review of the field begins with an overview of the phenomenology: how the Earth looks in the ultraviolet. Next the basic processes leading to excitation of atomic and molecular energy states are discussed. These concepts are developed from first principles and applied to selected examples of day and night airglow; a detailed review of radiation transport theory is included. This is followed by a comprehensive examination of the current status of knowledge of individual emission features seen in the airglow, in which atomic physics issues as well as relevant atmospheric observations of major and minor neutral and ionic constituents are addressed. The use of airglow features as remote sensing observables is then examined for the purpose of selecting those species most useful as diagnostics of the state of the thermosphere and ionosphere. Imaging of the plasmasphere and magnetosphere is also briefly considered. A summary of upcoming UV remote sensing missions is provided.
494 citations
TL;DR: A population of protons with energy of some tens of keV, called the ring current, is found near the equatorial region of the magnetosphere at several earth radii.
Abstract: A population of protons with energy of some tens of keV, called the ring current, is found near the equatorial region of the magnetosphere at several earth radii. During the main phase of geomagnetic storms the ring current shifts toward lower L values into the region of the plasmapause, which is characterized by steep gradients in the plasma density. This interaction together with an anisotropic pitch angle distribution leads to ring current instability and the growth of ion cyclotron wave turbulence. As wave energy is dissipated in the ambient electron gas by Landau damping, the plasmapause electron temperature is raised to a few electron volts, and a substantial temperature gradient is created with respect to the ionosphere. The energy transferred to the ionosphere by pitch angle scattering in the low collision frequency region and by heat conduction in the collision-dominated regime raises the ionospheric electron temperature to several thousand degrees. Therefore an appreciable number of electrons in the high-energy tail of the Maxwellian distribution, i.e., electrons with energy greater than 2 eV, exist in the F region of the ionosphere at about 400 km, where atomic oxygen is the dominant neutral gas constituent. Two eV is the threshold for excitation of oxygen atoms to the metastable ¹D level, and these O(¹D) atoms emit 6300-A radiation, the signature of stable auroral red (SAR) arcs. Although the energy input rate required to produce electron temperatures sufficient to cause average SAR arcs is less than 0.1 erg cm−2 s−1, the energy radiated in the red line is only about 0.003 erg cm−2 s−1. Thus an SAR arc is an optical manifestation of a slow release of energy from the magnetosphere during a geomagnetic storm. Energetically it is small in comparison with high-latitude auroral processes.
229 citations
TL;DR: In this article, it was shown that most of the N2 molecules excited to singlet states in the 12.5-14.86 eV range are depopulated by predissociation and not by the emission of EUV photons and that this is the principal mechanism by which N2 is dissociated by solar EUV absorption and by electron impact.
229 citations
TL;DR: In this paper, the relationship between three important middle UV auroral emissions, the electron energy spectrum, and the neutral atmosphere was examined, and calculated emission rates for the Vegard-Kaplan and second positive band systems of N2 and the O I (¹S → ³P) 2972 A line.
Abstract: In this paper we examine the relationship between three important middle UV auroral emissions, the electron energy spectrum, and the neutral atmosphere. We display calculated emission rates for the Vegard-Kaplan and second positive band systems of N2 and the O I (¹S → ³P) 2972 A line. All three features are proportional to the incoming energy flux, but they have different dependences on the characteristic energy of the incident electron spectrum and on the concentration of atomic oxygen. Therefore, in principle, observations of the intensities of these three emission features could be used to characterize the incident electron spectrum. Unfortunately, uncertainties in the chemistry of the ¹S state of atomic oxygen and the A³Σu+ state of nitrogen make it difficult to use such observations quantitatively. We discuss these uncertainties and possible alternative far ultraviolet features such as O I 1356 A and 1304 A and the N2 Lyman-Birge-Hopfield bands.
172 citations
TL;DR: In this paper, a comparison of the measured emission probabilities with theoretical values based on Franck-Condon factors for direct excitation was made, and molecular branching ratios were used to extend the optical calibration from the blackbody region to the vacuum ultraviolet.
Abstract: Emission cross sections and band emission probabilities have been measured for the fourth positive system (A1Π→X1Σ+) and the Cameron system (a3Π→X1Σ+) of CO and the first negative system (B2Σ+→ X2Σ+) and the comet tail system (A2Π→X2Σ+) of CO+ by electron beam excitation of CO from threshold to 300 eV. Excitation cross sections have been measured for CI, CII, and OI multiplets produced by dissociative excitation of CO. A comparison of the measured emission probabilities with theoretical values based on Franck—Condon factors for direct excitation was made. Molecular branching ratios were used to extend the optical calibration from the blackbody region to the vacuum ultraviolet.
161 citations