Abstract :
[en] We have observed electron impact fluorescence from CO2 to excite the Cameron bands (CBs), CO (a 3Π → X 1Σ+; 180-280 nm), the first-negative group (1NG) bands, CO+ (B 2Σ+ → X 2Σ+; 180-320 nm), the fourth-positive group (4PG) bands, CO (A 1Π → X 1Σ+; 111-280 nm), and the UV doublet, CO2+ ( B 2Σ u + → X 2Π g ; 288.3 and 289.6 nm) in the ultraviolet (UV). This wavelength range matches the spectral region of past and present spacecraft equipped to observe UV dayglow and aurora emissions from the thermospheres (100-300 km) of Mars and Venus. Our large vacuum system apparatus is able to measure the emission cross sections of the strongest optically forbidden UV transitions found in planetary spectra. Based on our cross-sectional measurements, previous CB emission cross-sectional errors exceed a factor of 3. The UV doublet lifetime is perturbed through B 2Σu + − A 2Π u spin-orbit coupling. Forward modeling codes of the Mars dayglow have not been accurate in the mid-UV due to systematic errors in these two emission cross sections. We furnish absolute emission cross sections for several band systems over electron energies 20-100 eV for CO2. We present a CB lifetime, which together with emission cross sections, furnish a set of fundamental physical constants for electron transport codes such as AURIC (Atmospheric Ultraviolet Radiance Integrated Code). AURIC and Trans-Mars are used in the analysis of UV spectra from the Martian dayglow and aurora.
Funding text :
This work was primarily performed at the Laboratory for Atmospheric and Space Physics (LASP), University of Colorado (CU) Boulder, and the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under a contract with the National Aeronautics and Space Administration (NASA). We gratefully acknowledge financial support through NASA's Solar System Workings (SSW), and the National Science Foundation (NSF) GEO-AGS Aeronomy program, NSF award number 2031349. R.A.L. thanks the Boulder Solar Alliance NSF REU program for past support. J-C.G. is supported by the PRODEX program managed by the European Space Agency (ESA) with help from the Belgian Federal Science Policy Office (BELSPO). We thank Karl Hubbell for technical support and Bruce Jakosky, and the MAVEN team, for the usage of the IUVS Optical-Engineering Unit (OEU). U.S. government sponsorship is acknowledged.
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