Nuclear Resonance Photon Scattering Studies of N₂ Adsorbed on Grafoil and of NaNO₂ Single Crystal

The nuclear resonance photon scattering (NRPS) from ¹⁵N₂ adsorbed on graphite was investigated. The resonantly scattered intensities from the 6324 keV level of ¹⁵N with the photon beam parallel and perpendicular to the adsorbing grafoil planes was measured at 140 K and coverages below 0.7 monolayers (ML), where the ¹⁵N₂ occur in the vapor phase. The data were used for deducing the out-of-plane tilt angle of adsorbed N₂ relative to the graphite surface and the results were compared with grand canonical Monte Carlo (GCMC) calculations. Using the same method, a single crystal of NaNO₂ was studied by measuring the scattering intensities with the nitrite planes aligned parallel and perpendicular to the photon beam. At 80 K, a huge anisotropy (R ≈ 3.6) was observed, caused by the anisotropy in the zero-point motion of the internal modes of vibration of the NO₂ ion. The variation of the scattering intensity from a powdered isotopic ¹⁵NaNO₂ sample versus T in the range 12 K to 297 K was also measured and explained by accounting for the internal and external vibrational modes in NaNO₂.