Laboratory Study of the Cameron Bands, the First Negative Bands, and Fourth Positive Bands in the Middle Ultraviolet 180–280 nm by Electron Impact Upon CO

Abstract

We have analyzed medium‐resolution (full width at half maximum, FWHM = 1.2 nm), Middle UltraViolet (MUV; 180–280 nm) laboratory emission spectra of carbon monoxide (CO) excited by electron impact at 15, 20, 40, 50, and 100 eV under single‐scattering conditions at 300 K. The MUV emission spectra at 100 eV contain the Cameron Bands (CB) CO(a 3Π → X 1Σ+), the fourth positive group (4PG) CO(A 1Π → X 1Σ+), and the first negative group (1NG) CO+(B 2Σ+ → X 2Σ) from direct excitation and cascading‐induced emission of an optically thin CO gas. We have determined vibrational intensities and emission cross sections for these systems, important for modeling UV observations of the atmospheres of Mars and Venus. We have also measured the CB “glow” profile about the electron beam of the long‐lived CO (a 3Π) state and determined its average metastable lifetime of 3 ± 1 ms. Optically allowed cascading from a host of triplet states has been found to be the dominant excitation process contributing to the CB emission cross section at 15 eV, most strongly by the d 3Δ and a' 3Σ+ electronic states. We normalized the CB emission cross section at 15 eV electron impact energy by multilinear regression (MLR) analysis to the blended 15 eV MUV spectrum over the spectral range of 180–280 nm, based on the 4PG emission cross section at 15 eV that we have previously measured (Ajello et al., 2019, https://doi.org/10.1029/2018ja026308). We find the CB total emission cross section at 15 eV to be 7.7 × 10−17 cm2.

Discrete Aurora on Mars: Spectral Properties, Vertical Profiles, and Electron Energies

“…The peak of the e + CO 2 excitation cross section was determined to reach 2.4 × 10 −16 cm 2 at 80 eV by Erdman and Zipf (1983) but several authors have used a value 2-3 times smaller. The e + CO cross section has been re-measured recently as equal to 7.7 × 10 −17 cm 2 at 15 eV (Lee et al, 2021). The production rate…”

“…The peak of the e + CO 2 excitation cross section was determined to reach 2.4 × 10 −16 cm 2 at 80 eV by Erdman and Zipf (1983) but several authors have used a value 2–3 times smaller. The e + CO cross section has been re‐measured recently as equal to 7.7 × 10 −17 cm 2 at 15 eV (Lee et al., 2021). The production rate of the B 2 Σ u + state is given by: where n is the CO 2 or CO number density, is the electron energy spectrum, and is the excitation cross section of the B 2 Σ u + state for CO 2 or CO.…”

Laboratory Study of the Cameron Bands and UV Doublet in the Middle Ultraviolet 180–300 nm by Electron Impact upon CO2 with Application to Mars

“…at 288.3 and 289.6 nm) band systems, require MUV emission cross sections of CO 2 to complement our recent emission cross-sectional studies of CO by electron impact (Lee et al 2021). Electron excitation of CO and CO 2 can produce the same MUV band systems, but with unique vibrational distributions and different rotational thermal energies.…”

“…This failure precipitated a controversy in the literature that has persisted for decades, due to the dichotomy between terrestrial airglow observations and model calculations (Cartwright 1978;Budzien et al 1994;Eastes & Dentamaro 1996;Eastes 2000). We have, for the first time, measured the UV forbidden LBH emissions at the University of Colorado with a large (1.5 m diameter chamber) vacuum system apparatus, using a long focal length electrostatic electron gun at low electron energy (10-200 eV), providing a long optical path length without excited-molecule deactivation from wall collisions (Ajello et al 2017(Ajello et al , 2019(Ajello et al , 2020Lee et al 2021).…”

“…The uncertainties of particular emission cross sections of UV transitions are greater than 100%. Our current set of UV laboratory spectra (35% accuracy) from low energy electron impact of CO, CO 2 , and N 2 provide a key opportunity for allowing more rigorous forward modeling of dayglow and aurora (Gronoff et al 2012;Ajello et al 2017Ajello et al , 2019Ajello et al , 2020Lee et al 2021).…”