This theoretical study uses ab initio quantum mechanical methods to investigate the electronic properties of ground and excited state sodium nitrate. We calculated electronic properties of the crystalline material for bulk, clean, and defected surfaces. The results of these calculations are used to explain the photoexcitation/desorption mechanism and support the conclusions of an earlier experimental investigation of the laser desorption of NO from single-crystal sodium nitrate. Ab initio periodic Hartree-Fock (PHF) theory was used to investigate the "molecular-ionic" character of crystalline sodium nitrate. The calculations indicate that the electronic structure of the bulk and cleavage surface are virtually identical (i.e., no shift in the resonant absorption profile is expected). This finding is consistent with the experimental results on the wavelength dependence of NO desorption yields for crystalline NaNO3. However, changes in the absorption manifold are found to accompany the removal of external nitrate oxygens (producing surface nitrite groups). The presence of these chemical defects causes states to appear in the band gap producing a red shift in the absorption band. Complete active space self-consistent field (CASSCF) calculations on NO3-, NO3, and NO2-, support the "local excitation model" of the pi*<-- pi(2) transition. These calculations also indicate that the transition energies of the nitrate ion are unaffected by the presence of the surrounding ions. The photoexcitation/dissociation mechanism of the nitrate ions in the crystal, however, differs from gas-phase processes in that the neutral photodetachment channel, observed in the gas phase, is energetically inaccessible in the solid due to the stabilization of ionic species (relative to neutrals) by the crystalline field.