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Title: Electron impact study of the 100 eV emission cross section and lifetime of the Lyman-Birge-Hopfield band system of N 2 : Direct excitation and cascade: Electron Impact Study of LBH Band System
Award ID(s):
1657686
NSF-PAR ID:
10059766
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
Journal of Geophysical Research: Space Physics
Volume:
122
Issue:
6
ISSN:
2169-9380
Page Range / eLocation ID:
6776 to 6790
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    We have measured the 30 and 100 eV far ultraviolet (FUV) emission cross sections of the optically allowed Fourth Positive Group (4PG) band system (A1Π → X1Σ+) of CO and the optically forbidden O (5So → 3P) 135.6 nm atomic transition by electron‐impact‐induced‐fluorescence of CO and CO2. We present a model excitation cross section from threshold to high energy for theA1Π state, including cascade by electron impact on CO. TheA1Π state is perturbed by triplet states leading to an extended FUV glow from electron excitation of CO. We derive a model FUV spectrum of the 4PG band system from dissociative excitation of CO2, an important process observed on Mars and Venus. Our unique experimental setup consists of a large vacuum chamber housing an electron gun system and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission Imaging Ultraviolet Spectrograph optical engineering unit, operating in the FUV (110–170 nm). The determination of the total Oi(5So) at 135.6 nm emission cross section is accomplished by measuring the cylindrical glow pattern of the metastable emission from electron impact by imaging the glow intensity about the electron beam from nominally zero to ~400 mm distance from the electron beam. The study of the glow pattern of Oi(135.6 nm) from dissociative excitation of CO and CO2indicates that the Oi(5So) state has a kinetic energy of ~1 eV by modeling the radial glow pattern with the published lifetime of 180 μs for the Oi(5So) state.

     
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  2. null (Ed.)
    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 1Πg → X 1Σg+) 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 w 1Δu → a 1Πg), which are followed by a cascade induced transition a 1Πg → X 1Σg+. 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 a 1Πg state are enhanced by CIETs, and the emission cross sections of the LBH band system for direct and cascading-induced excitation are provided at 40, 100, and 200 eV 
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  3. Abstract

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