Photolysis of diatomic molecules as a source of atoms in planetary exospheres^⋆

¹ University of Helsinki, Department of Chemistry, PO Box 55, A.I. Virtanens Plats 1, 00014 Helsinki, Finland
e-mail: valievrashid@gmail.com
² Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, Lenin Avenue 30, Tomsk 634050, Russia
³ Sternberg Astronomical Institute, Moscow State University, 13, Universitetskij pr., 119234 Moscow, Russia
⁴ Tomsk State University, 36 Lenin Avenue, 634050 Tomsk, Russia
⁵ Tomsk State University of Control Systems and Radioelectronics, 40 Lenin Avenue, 634050 Tomsk, Russia
⁶ Image Analysis Group, Technical University of Dortmund, Otto-Hahn-Str. 4, 44227 Dortmund, Germany

Received: 3 July 2019
Accepted: 24 July 2019

Abstract

We calculated the cross sections of photolysis of OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF molecules using quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides are on the order of 10⁻¹⁸ cm². The lifetimes of photolysis for quiet Sun at 1 astronomical unit are estimated as 2.0 × 10⁵, 28, 5, 14, 2.1 × 10⁵, 225, 42, 52, 2 × 10⁶, 35 400, 486, and 30 400 s for OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF, respectively. We performed a comparison between values of photolysis lifetimes obtained in this work and in previous studies. Based on such a comparison, our estimations of photolysis lifetimes of OH, HCl, and HF have an accuracy of about a factor of 2. We determined typical kinetic energies of main peaks of photolysis-generated metal atoms. Impact-produced LiO, NaO, KO, NaCl, and KCl molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight, while other considered molecules are more stable against destruction by photolysis.