Authors: Colognesi, D. | Andreani, C. | Degiorgi, E.
We have studied two “ice-like” systems, H2 S and HCl, which, despite their molecular simplicity, exhibit a rich polymorphism in solid phase. We performed incoherent neutron scattering measurements employing a new crystal-analyzer inverse-geometry neutron spectrometer, TOSCA-I. After a detailed data reduction procedure, we devised a technique aiming to estimate and remove the multi-phonon part of the spectra. Finally, the H-projected phonon densities of states, ZH (ω), were extracted and the respective H mean squared displacements, 〈u2 〉H , determined. These ZH (ω) show good statistical accuracy and resolution and represent an important benchmark for future lattice-dynamics simulations and phonon dispersion
…curve measurements. Since some thermal softening of the phonon modes was visible in both H2 S and HCl, we tried to quantify this anharmonic effect through the zero-point proton mean squared displacement, 〈u2 inter 〉H,0 , and the zero-point proton mean kinetic energy, 〈Ek,inter 〉H,0 . Finally, approximate Grüneisen parameters for 〈u2 inter 〉H,0 and 〈Ek,inter 〉H,0 were calculated exploiting D2 S neutron diffraction data.
Keywords: Hydrogen bonded solids, phonon density of states, incoherent inelastic neutron scattering, crystal-analyzer inverse-geometry spectrometer, hydrogen sulfide, hydrogen chloride
Citation: Journal of Neutron Research,
vol. 11, no. 3, pp. 123-143, 2003
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