N₂(A) in the Terrestrial Thermosphere

Abstract

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, N 2 (A 3 Σ + u ), and atomic oxygen. A steady-state model for the N 2 (A) vibrational distribution in the terrestrial thermosphere is here described and validated by comparison with N 2 A-X, Vegard-Kaplan dayglow spectra from the Ionospheric Spectroscopy and Atmospheric Chemistry spectrograph. A computationally cheaper method is needed for implementation of the N 2 (A) chemistry into time-dependent thermospheric models. It is shown that by scaling the photoelectron impact production of ionized N 2 by a Gaussian centered near 100 km, the level-specific N 2 (A) production rates between 100 and 200 km can be reproduced to within an average of 5%. This scaling, and thus the N 2 electron 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 N 2 electron-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. (2009 https://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 denoted J05M09. Upon updating these cross sections it is found that (1) the total N 2 triplet excitation rate remains nearly constant; (2) the steady state N 2 (A) vibrational distribution is shifted to higher levels; (3) the total N 2 singlet excitation rate responsible for the Lyman-Birge-Hopfield emission is reduced by 33%. It is argued that adopting the J05M09 cross sections supports (1) the larger X-ray fluxes measured by the Student Nitric Oxide Explorer (SNOE) and (2) a temperature-independent N 2 (A)+O reaction rate coefficient. Plain Language Summary Plain Language Summary Theoretical modeling of nitric oxide(NO) in the thermosphere has historically been underestimated in comparison with measurements. A new chemical source of NO has been proposed, but to accurately incorporate it into existing models requires a fast way of calculating the electronic and vibrational temperature of the reacting nitrogen gas. It is shown in this work that this can be done by using the N 2 ionization rate as a proxy and that this has the added benefit of being independent of existing unknowns regarding the solar flux at X-ray wavelengths. These results are further discussed in light of recent measurements by the atomic and molecular physics community concerning standard thermospheric diagnostic emissions, particularly the N 2 Lyman-Birge-Hopfield emission. Use of these new cross sections in thermospheric models is found to have significant implications for our understanding of the energy budge...

Zero-dimensional and pseudo-one-dimensional models of atmospheric-pressure plasma jets in binary and ternary mixtures of oxygen and nitrogen with helium background

“…The value is confirmed for the vibrational ground state N 2 (A 3 Σ, v = 0). Note that a much larger value is observed for the higher vibrational quantum numbers N 2 (A 3 Σ, v > 0) [96][97][98][99][100][101]. Furthermore, the virtually identical NO density is obtained between the measurements and the simulations considering the reactive quenching of multiple N 2 electronically excited states by O( 3 P) [29].…”

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

“…4PG, 1NG, and Cameron Band cross sections as a measured in this work as a function of energy. Data points represent the measured cross sections from this study, and intermediate values were interpolated using the analytic fit formulation described in Yonker and Bailey (2020). The coefficients used in this fit are given in Table 5.…”

“…The measurements reported in this study fill this gap and open a new possibility to map the CO density distribution. Yonker and Bailey (2020) The CO in both the Mars and thermospheres is expected to be variable since it is submitted redistribution by the global circulation following CO 2 dissociation (Jain et al, 2015). Therefore, spatial variations in the spectral distribution of the CB in the upper thermosphere could be an indicator of seasonal, latitudinal, or local time changes in the CO/CO 2 mixing ratio.…”

“…We show in Figure 7 the compilation of our results for the 1NG bands, the 4PG, and CB from our MUV work and list in Table 4 the new recommended cross sections for the CB and 1NG bands based on the cross section of the 4PG system above 180 nm, which is the absolute calibration standard used in this experiment (Ajello et al, 2019). Continuous cross section curves over energy were analytically fit to the calculated values with a general, unbound MLR according to the formulation in Appendix A of Yonker and Bailey (2020). The coefficients used for the analytic fit are given in Table 5.…”

Triplet state harvesting and search for forbidden transition intensity in the nitrogen molecule

“…The relatively long radiative lifetime enables N 2 (A ) to participate in collisions with the main background gases of the MLT region and to produce chemical reactions with N 2 , O 2 , N, and O species. In particular, the reactions are the most important ones ( Yonker and Bailey, 2019 ). A recent steady-state MLT model developed for the N 2 (A ) vibrational distribution in the terrestrial atmosphere is supported by comparison with the Vegard–Kaplan dayglow emission from atmospheric photochemistry and ionospheric spectroscopy measurements ( Yonker and Bailey, 2019 ).…”