Reexamination of important N/sub 2/ cross sections by electron impact with application to the dayglow: The Lyman-Birge-Hopfield band System and N I (119. 99 nm)

Journal Article · Tue Oct 01 00:00:00 EDT 1985 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA090iA10p09845· OSTI ID:6336761

Ajello, J M; Shemansky, D E

The far ultraviolet emission spectrum (120 to 210 nm) of electron-excited N/sub 2/ has been obtained in a crossed-beam laboratory experiment. The cross section of the Lyman-Birge-Hopfield (LBH) band system (a/sup 1/Pi/sub g/..-->..X/sup 1/..sigma../sub g//sup +/) has been remeasured using experimental techniques we have previously developed for this metastable transition. The improved laboratory data set for the a/sup 1/Pi/sub g/ state allows a determinatoin emission of the excitation emission and predissociation cross section from threshold to 200 eV for use in planetary atmosphere models of the dayglow and aurora. An analytic fit to the experimental cross section allows accurate estimates to arbitrarily high excitation energy. The close agreement in both energy dependence and absolute cross section values between the emission measurements, presented here, and published electron scattering results shows cascade is small (<5%). The total excitation cross section for the N/sub 2/a/sup 1/Pi/sub g/ state is estimated to be 6.22 +- 1.37 x 10/sup -18/ cm/sup 2/ at 100 eV. The absence of emission bands for ..nu..'> or =7 suggests the predissociation yield is unity. The excitation function of each vibrational level is found to have the same shape to within 5%. In the low-energy region, epsilon<20 eV, differences in excitation threshold lead to a significant departure of the relative vibrational cross sections from the Franck-Condon distribution. Thus the relative LBH vibrational population distribution in a planetary dayglow or aurora is affected by the energy distribution of the electron flux: and we show that atmospheric models need to include this threshold effect.

• Research Organization: Jet Propulsion Laboratory, California Institute of Technology, Pasadena
• OSTI ID: 6336761
• Journal Information: J. Geophys. Res.; (United States), Vol. 90:A10
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ELECTRON-MOLECULE COLLISIONS
EXCITATION
NITROGEN
FAR ULTRAVIOLET RADIATION
AIRGLOW
CROSS SECTIONS
EMISSION SPECTRA
ENERGY DEPENDENCE
EV RANGE
COLLISIONS
ELECTROMAGNETIC RADIATION
ELECTRON COLLISIONS
ELEMENTS
ENERGY RANGE
ENERGY-LEVEL TRANSITIONS
MOLECULE COLLISIONS
NONMETALS
RADIATIONS
SPECTRA
ULTRAVIOLET RADIATION
640304* - Atomic
Molecular &amp; Chemical Physics- Collision Phenomena