Nuclear Resonance Photon Scattering Studies of N(2) Adsorbed on Grafoil and of NaNO(2) Single Crystal

The nuclear resonance photon scattering (NRPS) from (15)N(2) adsorbed on graphite was investigated. The resonantly scattered intensities from the 6324 keV level of (15)N 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 (15)N(2) occur in the vapor phase. The data were used for deducing the out-of-plane tilt angle of adsorbed N(2) 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 NaNO(2) 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 NO(2) ion. The variation of the scattering intensity from a powdered isotopic (15)NaNO(2) 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 NaNO(2).