  The electron-photon interaction (the spinor-vector field interaction) in the
de Sitter ambient space formalism is investigated in the first (leading order)
approximation. The interaction Lagrangian and the scattering matrix are
presented. In this approximation, the scattering matrix can be written as a
expansion of the interaction Lagrangian. The tree-diagram of electron-photon
scattering amplitude is calculated. Finally the Minkowski limit is considered.
