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- Title
The UV Spectrum of the Lyman‐Birge‐Hopfield Band System of N<sub>2</sub> Induced by Cascading from Electron Impact.
- Authors
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
- Abstract
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 (a1Πg→X1Σg+) of N2 excited by 30–200 eV electrons. The cascading transition begins with two processes: radiative and collision‐induced electronic transitions (CIETs) involving two states (a′1Σu− and w1Δu → a1Πg), which are followed by a cascade induced transition a1Πg→X1Σg+ 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 N2 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 a1Πg 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. Key Points: First imaging measurement of the electron‐impact N2 LBH cascade‐induced spectrum at energies of 30–200 eV is presentedCascading transition to the N2a‐state (a′ and w → a) from radiative and collision‐induced‐electronic transitions (CIETs)We present LBH band intensities at various pressures and electron impact direct and cascade LBH emission cross sections from 40–200 eV
- Subjects
ULTRAVIOLET spectra; SCATTERING (Physics); ELECTRON beams; FLUORESCENCE; EMISSIONS (Air pollution)
- Publication
Journal of Geophysical Research. Space Physics, 2020, Vol 125, Issue 3, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2019JA027546