The reaction of excess electrons at the surface of MgO with ammonia leads to surface ammoniated electrons analogous to those formed when alkali metals are dissolved in anhydrous ammonia. Surface excess electrons are found to be solvated by up to three ammonia molecules, and well-resolved CW and pulsed EPR spectra allow for a precise description of the unpaired electron spin density distribution over the solvent molecules. The large majority of the electron spin density resides in the first-shelf nitrogen fragments. HYSCORE spectra allow obtaining for the first time the full hyperfine interaction of the solvated electron with the ammonia protons, which is consistent with a small and negative spin density in the H-1 is orbital. Furthermore, the hyperfine and nuclear quadrupole tenors of the second-shell nitrogens could be unravelled.