Developing a numerical model of photo-emitted electron energy spectra and its applications

Since the Moon does not possess a dense atmosphere, its surface directly interacts with surrounding charged particles. In addition, photoelectrons and secondary electrons are emitted from the surface in response to incident photons and charged particles. To evaluate the direct interaction between the lunar surface and the charged particles, it is important to obtain the energy spectra of these particles, including photoelectrons. In this presentation, we introduce a numerical model of electrons emitted from the lunar surface due to solar irradiation. The input of the model is the solar irradiation flux, and it includes some physical and chemical parameters associated with photoemission. The model also considers Auger electrons, which are emitted from an atom following the emission of an inner-shell electron and possess characteristic energies. This model can be applied to various topics at the lunar surface, including surface charging. Surface charging is caused by incoming and outgoing currents and is characterized by the surface potential, which varies to balance incoming and outgoing electric currents. The lunar surface potential can be estimated by comparing model outputs with electron observations above the lunar surface. We also present applications of the model to potential estimation.