Mars and Venus Dayglow Studies Based Upon Laboratory Aeronomy from Electron Impact of CO2 for analysis of UV Observations by MAVEN, EMM, MEx, and VEx

We have developed a laboratory aeronomy program at the University of Colorado to study electron impact fluorescence of the Cameron Bands CO(a 3Π → X 1Σ+; 180-260 nm), the First-Negative (1NG) Bands CO+(B 2Σ+ → X 2Σ; 180-320 nm), the Fourth-Positive (4PG) Bands CO(A 1Π → X 1S+ ; 111-280 nm), and UV doublet CO2+ (B 2Σ → X 2Πg; at 288.3 and 289.6 nm) in the FUV and MUV (Far and Middle UltraViolet) from CO2, to match the spectral region of present and future spacecraft equipped to observe the UV dayglow of Mars (100-300 km). We have constructed a large vacuum system apparatus that has measured the emission cross sections of the strongest optically-forbidden transitions found in the Mars airglow and aurora, the Cameron Bands, as well as perturbed UV doublet and 4PG Bands. The chemistry of the upper atmospheres above 100 km in the evolution of Mars and Venus can be determined from the observation of the UV airglow spectra by MAVEN IUVS (Imaging UltraViolet Spectrograph) spanning 110-340 nm and by MEx SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) covering 118-320 nm. We emphasized the study of the Cameron Band emissions from electron impact dissociative excitation of CO2, an uncertain physical process in the ionosphere of Mars. Based on our current cross section measurements, previous estimates of Cameron Band emission cross sections are in error by a factor of three or more, and forward modeling codes of the Mars dayglow have not been accurate in the MUV in the past due to errors in these cross sections that are used to calculate excitation rates. The rotational levels of the CO a-state are found to be long-lived with a lifetime of ~1-5 ms, a lifetime measured from the laboratory radial glow profile about the electron beam and the additional intensity from the UV doublet emission from B~A state coupling. We plan to furnish absolute emission cross sections (cascade + direct excitation) from threshold (~10 eV) to 300 eVfor CO and CO2, a set of fundamental physical constants for electron transport codes such as AURIC (Atmospheric Ultraviolet Radiance Integrated Code; Evans et al., 2015) used in the analysis of dayglow spectra from the Martian dayglow and aurora by the MAVEN imaging spectrometer, Emirates Mars Mission, and SPICAM, as well as the Venus dayglow by SPICAV.