Optical Properties of Sodium Nitrate in the Vacuum Ultraviolet Region

The reflectivity spectra of NaNO ₃ single crystal have been measured in the region from 4 to 12 eV with polarized light normally incident upon the cleaved surface (10\bar11). Two principal dielectric constants, \(\hat{\varepsilon}_{\text{o}}\) and \(\hat{\varepsilon}_{\text{e}}\), have been derived from the spectra with the application of the Kramers-Kronig relation and the equation of dielectric ellipsoid for uniaxial crystals. The profile of the absorption spectrum derived from the reflectivity is in good agreement with the absorption spectrum of thin films, particularly with respect to the bands at about 6 eV and 10.5 eV. It is found that the 6 eV band is active to light polarized perpendicularly to the c axis and the oscillator strength of the band is 0.4 ₉ per NO ₃ ^- molecule. These facts support the previous assignment that the absorption is due to π ₂ →π ^* ( A ₁ '→ E ') in NO ₃ ^- . The 10.5 eV band is found to be active to light polarized perpendicularly to the c axis, and is assigned to the electron transfer from the n ₂ ( e ') orbitals of NO ₃ ^- to the Na ⁺ –3s orbital.