Electronically excited molecular nitrogen in the upper and middle atmospheres of Titan and Earth
GC2024-STP061
Molecular nitrogen N2 is the main molecular gas in the atmospheres of the Earth, Titan (a moon of Saturn), Triton (a moon of Neptune) and Pluto. In the Earth's atmosphere, the second gas in total concentration is molecular oxygen O2; in the atmospheres of the other mentioned planets it is methane CH4. We study the kinetics of the triplet A3Σu+, B3Πg, W3Δu, B'3Σu–, C3Πu states of molecular nitrogen at altitudes of the upper (700-1200 km) and middle (50-250 km) atmosphere of Titan during the precipitation of solar UV photons and galactic cosmic rays into the atmosphere. The calculations take into account intramolecular and intermolecular electron energy transfer during inelastic collisions of electronically excited molecular nitrogen with N2, CH4 and CO molecules. The interaction constants of electronically excited molecular N2(A3Σu+) with N2 and CO molecules are calculated according to quantum chemical approximations and show good agreement with the available experimental data [1]. It is shown that there is a significant contribution of electronically excited N2 in the excitation of CO(a3Π) at the altitudes of 700-1200 km of the Titan’s upper atmosphere. The interaction of electronically excited N2 molecules with molecules of methane CH4, acetylene C2H2, ethylene C2H4, ethane C2H6 in the Titan’s middle atmosphere at altitudes of 50-250 km was studied. The dominance of reactions with metastable molecular nitrogen N2(A3Σu+) in the formation of C2H and C2H3 radicals at these altitudes was shown for the first time [2]. Similar kinetic calculations involving triplet electron-excited molecular nitrogen were carried out for the Earth’s middle atmosphere of 30-80 km during the precipitation of high-energy relativistic electrons into the atmosphere [3]. The interaction constants of metastable molecular nitrogen N2(A3Σu+) with oxygen molecules O2 were calculated and compared with the available experimental data [4]. The emission intensities of the bands of the first positive and second positive N2 systems during the precipitation of high-energy electrons were calculated. It is shown that there is a significant decrease in the emission intensities of the bands of the first positive system with decreasing altitude due to the influence of collision processes on the populations of vibrational levels of the N2(B3Πg) molecule. The influence of intermolecular processes of energy transfer from N2(A3Σu+) on the formation of singlet oxygen and the emission of the Atmospheric and Infrared atmospheric bands of O2 at altitudes of the Earth’s middle atmosphere was studied.
[1] A.S. Kirillov, Chem. Phys. Lett. 643 (2016) 131.
[2] A.S. Kirillov, R. Werner, and V. Guineva, Bull. Russ. Acad. Sci.: Physics, 87 (2023) 985.
[3] A.S. Kirillov and V.B. Belakhovsky, Geophys. Res. Lett., 46 (2019) 7734.
[4] A.S. Kirillov and V.B. Belakhovsky, J. Geophys. Res.: Atmos., 126 (2021) e2020JD033177.