  The Schr\" odinger picture of the Dirac quantum mechanics is defined in
charts with spatially flat Robertson-Walker metrics and Cartesian coordinates.
The main observables of this picture are identified, including the interacting
part of the Hamiltonian operator produced by the minimal coupling with the
gravitational field. It is shown that in this approach new Dirac quantum modes
on de Sitter spacetimes may be found analytically solving the Dirac equation.
