Photolysis of metal oxides as a source of atoms in planetary exospheres

Abstract

The cross sections of photolysis of LiO, NaO, KO, MgO, and CaO molecules have been calculated by the use of quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides have the order of 10−17 cm2, and for alkaline earth metal monoxides these values are less on 1–2 orders of the magnitude. The lifetimes of photolysis at 1 astronomical unit are estimated as 5, 3, 60, 70, and 3,000 s for LiO, NaO, KO, MgO, and CaO, respectively. Typical kinetic energies of main peaks of photolysis-generated metal atoms are determined. Impact-produced LiO, NaO, KO, and MgO molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight while CaO molecule is more stable against destruction by photolysis. Photolysis-generated metal atoms in planetary exospheres can be detected by performing high-resolution spectral observations of velocity distribution of exospheric metal atoms.