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The UV Spectrum of the Lyman‐Birge‐Hopfield Band System of N 2 Induced by Cascading from Electron Impact
Author(s) -
Ajello Joseph M.,
Evans J. Scott,
Veibell Victoir,
Malone Charles P.,
Holsclaw Greg M.,
Hoskins Alan C.,
Lee Rena A.,
McClintock William E.,
Aryal Saurav,
Eastes Richard W.,
Schneider Nicholas
Publication year - 2020
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027546
Subject(s) - atomic physics , electron , excitation , excited state , cascade , electron scattering , scattering , radiative transfer , atomic electron transition , physics , electron ionization , cathode ray , chemistry , spectral line , optics , ionization , ion , quantum mechanics , chromatography , astronomy
We have measured in the laboratory the far ultraviolet (FUV: 125.0–170.0 nm) cascade‐induced spectrum of the Lyman‐Birge‐Hopfield (LBH) band system ( a 1 Π g → X 1 Σ g + ) of N 2 excited by 30–200 eV electrons. The cascading transition begins with two processes: radiative and collision‐induced electronic transitions (CIETs) involving two states ( a ′ 1 Σ u − and w 1 Δ u → a 1 Π g ), which are followed by a cascade induced transition a 1 Π g → X 1 Σ g + at the single‐scattering pressures employed here. Direct excitation to the a ‐state produces a confined LBH spectral glow pattern around an electron beam. We have spatially resolved the electron‐induced glow pattern from an electron beam colliding with N 2 at radial distances of 0–400 mm at three gas pressures. This imaging measurement is the first to isolate spectral measurements in the laboratory of single‐scattering electron‐impact‐induced fluorescence from two LBH emission processes: direct excitation, which is strongest in emission near the electron beam axis; and cascading‐induced, which is dominant far from the electron beam axis. The vibrational populations for vibrational levels from v′ = 0–2 of the a 1 Π g state are enhanced by radiative cascade and CIETs, and the emission cross sections of the LBH band system for direct and cascading‐induced excitation are provided at 40, 50, 100, and 200 eV.