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1. Laboratory Study of the Cameron Bands and UV Doublet in the Middle Ultraviolet 180–300 nm by Electron Impact upon CO 2 with Application to Mars

   https://doi.org/10.3847/1538-4357/ac88c8  

   Lee, Rena A. ; Ajello, Joseph M. ; Malone, Charles P. ; Evans, J. Scott ; Veibell, Victoir ; Holsclaw, Gregory M. ; McClintock, William E. ; Hoskins, Alan C. ; Jain, Sonal K. ; Gérard, Jean-Claude ; et al ( October 2022 , The Astrophysical Journal)

   We have observed electron impact fluorescence from CO₂to excite the Cameron bands (CBs), CO (a³Π →X¹Σ⁺; 180–280 nm), the first-negative group (1NG) bands, CO⁺(B²Σ⁺→X²Σ⁺; 180–320 nm), the fourth-positive group (4PG) bands, CO (A¹Π →X¹Σ⁺; 111–280 nm), and the UV doublet, CO₂⁺($\tilde{B}{}^2{\mathrm{\Sigma }}_u^{+}\to \tilde{X}{}^2{\mathrm{\Pi }}_g;$288.3 and 289.6 nm) in the ultraviolet (UV). This wavelength range matches the spectral region of past and present spacecraft equipped to observe UV dayglow and aurora emissions from the thermospheres (100–300 km) of Mars and Venus. Our large vacuum system apparatus is able to measure the emission cross sections of the strongest optically forbidden UV transitions found in planetary spectra. Based on our cross-sectional measurements, previous CB emission cross-sectional errors exceed a factor of 3. The UV doublet lifetime is perturbed through$\tilde{B}{}^2{\mathrm{\Sigma }}_u^{+}-\tilde{A}{}^2{\mathrm{\Pi }}_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.

    

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2. UV Study of the Fourth Positive Band System of CO and O i 135.6 nm From Electron Impact on CO and CO 2

   https://doi.org/10.1029/2018JA026308  

   Ajello, J. M. ; Malone, C. P. ; Evans, J. S. ; Holsclaw, G. M. ; Hoskins, A. C. ; Jain, S. K. ; McClintock, W. E. ; Liu, X. ; Veibell, V. ; Deighan, J. ; et al ( April 2019 , Journal of Geophysical Research: Space Physics)

   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 (⁵S^o → 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(⁵S^o) 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(⁵S^o) state has a kinetic energy of ~1 eV by modeling the radial glow pattern with the published lifetime of 180 μs for the Oi(⁵S^o) state.

    

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3. N 2 (A) in the Terrestrial Thermosphere

   https://doi.org/10.1029/2019JA026508  

   Yonker, Justin D. ; Bailey, Scott M. ( January 2020 , Journal of Geophysical Research: Space Physics)

   Recent work has indicated the presence of a nitric oxide (NO) product channel in the reaction between the higher vibrational levels of the first electronically excited state of molecular nitrogen, N₂(A), and atomic oxygen. A steady‐state model for the N₂(A) vibrational distribution in the terrestrial thermosphere is here described and validated by comparison with N₂A‐X, Vegard‐Kaplan dayglow spectra from the Ionospheric Spectroscopy and Atmospheric Chemistry spectrograph. A computationally cheaper method is needed for implementation of the N₂(A) chemistry into time‐dependent thermospheric models. It is shown that by scaling the photoelectron impact production of ionized N₂by a Gaussian centered near 100 km, the level‐specific N₂(A) production rates between 100 and 200 km can be reproduced to within an average of 5%. This scaling, and thus the N₂electron impact ionization/excitation ratio, is nearly independent of existing uncertainties in the 2–20 nm solar soft X‐ray irradiance. To investigate this independence, the N₂electron‐impact excitation cross sections in the GLOW photoelectron model are replaced with the results of Johnson et al. (2005,https://doi.org/10.1029/2005JA011295) and the multipart work of Malone et al. (2009https://doi.org/10.1103/PhysRevA.79.032704) (Malone, Johnson, Young, et al., 2009,https://doi.org/10.1088/0953-4075/42/22/225202; Malone, Johnson, Kanik, et al., 2009,https://doi.org/10.1103/PhysRevA.79.032705; Malone et al., 2009,https://doi.org/10.1103/PhysRevA.79.032704), together denotedJ05M09. Upon updating these cross sections it is found that (1) the total N₂triplet excitation rate remains nearly constant; (2) the steady state N₂(A) vibrational distribution is shifted to higher levels; (3) the total N₂singlet excitation rate responsible for the Lyman‐Birge‐Hopfield emission is reduced by 33%. It is argued that adopting theJ05M09 cross sections supports (1) the larger X‐ray fluxes measured by the Student Nitric Oxide Explorer (SNOE) and (2) a temperature‐independent N₂(A)+O reaction rate coefficient.

    

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4. A Missing Piece of the E‐Region Puzzle: High‐Resolution Photoionization Cross Sections and Solar Irradiances in Models

   https://doi.org/10.1029/2023JA031870  

   Soto, Emmaris ; Evans, J. Scott ; Meier, R. R. ; Tashiro, Motomichi ; Sakib, MD. Nazmus ; Yiğit, Erdal ( April 2024 , Journal of Geophysical Research: Space Physics)

   Most ionospheric models cannot sufficiently reproduce the observed electron density profiles in the E‐region ionosphere, since they usually underestimate electron densities and do not match the profile shape. Mitigation of these issues is often addressed by increasing the solar soft X‐ray flux which is ineffective for resolving data‐model discrepancies. We show that low‐resolution cross sections and solar spectral irradiances fail to preserve structure within the data, which considerably impacts radiative processes in the E‐region, and are largely responsible for the discrepancies between observations and simulations. To resolve data‐model inconsistencies, we utilize new high‐resolution (0.001 nm) atomic oxygen (O) and molecular nitrogen (N₂) cross sections and solar spectral irradiances, which contain autoionization and narrow rotational lines that allow solar photons to reach lower altitudes and increase the photoelectron flux. This work improves upon Meier et al. (2007,https://doi.org/10.1029/2006gl028484) by additionally incorporating high‐resolution N₂photoionization and photoabsorption cross sections in model calculations. Model results with the new inputs show increased O⁺production rates of over 500%, larger than those of Meier et al. (2007,https://doi.org/10.1029/2006gl028484) and total ion production rates of over 125%, while production rates decrease by ∼15% in the E‐region in comparison to the results obtained using the cross section compilation from Conway (1988,https://apps.dtic.mil/sti/pdfs/ADA193866.pdf). Low‐resolution molecular oxygen (O₂) cross sections from the Conway compilation are utilized for all input cases and indicate that is a dominant contributor to the total ion production rate in the E‐region. Specifically, the photoionization contributed from longer wavelengths is a main contributor at ∼120 km.

    

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5. Going beyond the borders: pyrrolo[3,2- b ]pyrroles with deep red emission

   https://doi.org/10.1039/d1sc05007a  

   Tasior, Mariusz ; Kowalczyk, Paweł ; Przybył, Marta ; Czichy, Małgorzata ; Janasik, Patryk ; Bousquet, Manon H. ; Łapkowski, Mieczysław ; Rammo, Matt ; Rebane, Aleksander ; Jacquemin, Denis ; et al ( December 2021 , Chemical Science)

   A two-step route to strongly absorbing and efficiently orange to deep red fluorescent, doubly B/N-doped, ladder-type pyrrolo[3,2- b ]pyrroles has been developed. We synthesize and study a series of derivatives of these four-coordinate boron-containing, nominally quadrupolar materials, which mostly exhibit one-photon absorption in the 500–600 nm range with the peak molar extinction coefficients reaching 150 000, and emission in the 520–670 nm range with the fluorescence quantum yields reaching 0.90. Within the family of these ultrastable dyes even small structural changes lead to significant variations of the photophysical properties, in some cases attributed to reversal of energy ordering of alternate-parity excited electronic states. Effective preservation of ground-state inversion symmetry was evidenced by very weak two-photon absorption (2PA) at excitation wavelengths corresponding to the lowest-energy, strongly one-photon allowed purely electronic transition. π-Expanded derivatives and those possessing electron-donating groups showed the most red-shifted absorption- and emission spectra, while displaying remarkably high peak 2PA cross-section ( σ 2PA ) values reaching ∼2400 GM at around 760 nm, corresponding to a two-photon allowed higher-energy excited state. At the same time, derivatives lacking π-expansion were found to have a relatively weak 2PA peak centered at ca. 800–900 nm with the maximum σ 2PA ∼50–250 GM. Our findings are augmented by theoretical calculations performed using TD-DFT method, which reproduce the main experimental trends, including the 2PA, in a nearly quantitative manner. Electrochemical studies revealed that the HOMO of the new dyes is located at ca . −5.35 eV making them relatively electron rich in spite of the presence of two B − –N + dative bonds. These dyes undergo a fully reversible first oxidation, located on the diphenylpyrrolo[3,2- b ]pyrrole core, directly to the di(radical cation) stage. 

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