Dynamics of alpha-glycine from normal, C-deuterated and N-deutuered samples at 20 K has been investigated through high-resolution neutron-scattering experiments in the energy-transfer range 5-250 meV. Torsional peak of NH3+ is found to be split, an observation made for the first time using neutrons. The torsional potential is seen to be anharmonic. Coupling of other modes to the motion of hydrogen atoms of NH3+ and CH2 is discussed.

Dynamics of water molecules in Ba(ClO3)2 · H2O has been investigated through high resolution neutron scattering experiments at 6 K in the energy transfer region 5–200 meV. The libration peaks are found to be correlation split, an observation made for the first time using neutrons. The libration potential is seen to be anharmonic.

Bragg cut-off for\((10\bar 10)\) plane of polycrystalline beryllium of various lengths of 300 and 116 K has been measured with an energy resolution of 5 μeV. The natural width of the cut-off is 12.5±1.5 μeV, independent of temperature and length of beryllium and also of physical characteristics and certain metallurgical treatments of the powder. Such blocks of beryllium would be suitable for designing a ΔT-window spectrometer with resolution ⩾20 μeV. Bragg cut-offs corresponding to (0002) and\((10\bar 11)\) planes of beryllium have been separated for the first time. These can also be used for producing additional energy windows in a ΔT-window spectrometer, thus increasing its efficiency.

A high resolution neutron spectrometer making use of a AT-window filter for the analyser and time-of-flight technique for analysing incident neutron energy has been designed. The spectrometer will provide a continuously variable energy resolution AE from 40-50/~¢V at ~ 5230/~V. The range of energy transfer allowed is 1450 #eV to + 2950 ~eV and the range of wavevector transfer Q allowed is 0.82-3.06 A~. Depending on the resolution used, the counting rates are expected to vary from 28-60 x l03 counts/hr if one assumes 10% isotropic elastic scattering from the sample.

Inelastic neutron scattering experiments on normal N‐deuterated and fully deuterated glycine, normal and N‐deuterated alanine, L‐valine, L‐tyrosine and, L‐phenyl alanine at 100 K, are reported. Coupling of the external modes to different hydrogens is discussed.

Neutron inelastic scattering measurements have been performed on [(NH4)xK1−x]2SO4. It is shown that NH4+ preferentially occupies one of the two available inequivalent sites at smaller concentrations. NH4+ at the other site seems to be necessary for the occurance of ferroelectricity in these compounds.

Neutron scattering of cold neutrons from liquid silane at 137° K and 98°K is explained on the basis of a simple model. The rotational diffusion constant,D r, and the delay time,τ 0, after which rotational diffusion may be said to occur are derived on the basis of this model. At 137° K we getD r=0.22×1013 sec−1 andτ 0=0.68×10−13 sec. At 98°KD r (=0.06×1013 sec−1) is down by a factor of more than three butτ 0=(0.54×10−13 sec) shows only a small change. By comparison with data on liquid CH4 it is concluded that the law of corresponding states is not applicable for describing rotational dynamics of CH4 and SiH4. Rotational motions in SiH4 are more hindered than in CH4 at the same reduced temperature.

The scattering of 4.1 Å neutrons by liquid ammonia has been measured at 218 K in the angular range of 30–90° using the Trombay rotating crystal spectrometer. The experimental data, after correcting for multiple scattering, have been compared with model calculations, and it is shown that it is possible to get detailed information about the rotational correlation function on the basis of neutron experiments alone. The model assumes Langevin diffusion for translational motions. Rotational motions are described by means of an orientational correlation function which has a gaseous behaviour for times up toτ 0 and then changes over to a diffusive character with a rotational diffusion constantD r. Within the framework of the model the correlation function can be described withD r=0.28×1013sec−1 andτ 0=0.57×10−18sec. Corrections for multiple scattering and their dependence on model parameters are discussed.

Phonon frequencies in beryllium along the principal symmetry directions have been determined by means of the slow neutron inelastic scattering technique. The data are analysed in terms of a six-neighbour force constant model and the force constants are evaluated. It is concluded that strong tensor forces are present in beryllium and the importance of this finding to basic theories of lattice dynamics is pointed out.

The use of a filter-detector spectrometer for accurate measurements of phonon dispersion curves is demonstrated. Two possible approaches — the “average energy” and the “cut-off energy” — have been examined experimentally as well as theoretically and it is shown that the former approach is consistent and reliable.

We present dispersion curves for phonons along ΓKM in Be. It is shown that the ordering of the branches corresponding to the phonon modes polarized in the basal plane at the symmetry point K provides a simple and direct qualitative criterion for the presence of tensor forces. The existing pseudopotential calculations of the dynamics are inherently incapable of explaining these results. Generalizations required in the theory are mentioned.

AbstractThe frequency distribution function, g(ω), for solid ammonia has been derived from neutron inelastic scattering experiments at 106° K. It is used to calculate the specific heat and to analyse it in terms of Debye temperatures for translational and rotational parts. A comparison of the Debye temperatures with those obtained from the measured specific heat shows an excellent agreement up to 100°K, suggesting that the anharmonicity is not large below this temperature. Translational and rotational moments of the frequency distribution function calculated from the obtained g(ω) and the specific heat data are found to agree within about 10%.

Par diffusion inélastique des neutrons, on a étudié les movements de libration de la molécule d'eau dans les monocristaux Ba(ClO 3 ) 2 .H 2 O et K 2 C 2 O 4 .H 2 O. L'assignation des pics observés est discutée dans le cadre des caractèristiques qui influent l'intensité, c'est-à-dire: l'orientation du cristal et le vecteur de polarisation des modes de libration.

AbstractNeutron inelastic scattering studies on polycrystalline samples of K2C2O4 · H2O, Ba(ClO3)2 · H2O, Li2SO4 · H2O, CaSO4 · 2H2O, CuCl2 · 2H2O, and BeSO4 · 4H2O have been performed at room temperature and 100°K with the aim to observe the librational frequencies in these hydrates. Deuterated salts were studied to confirm the librational modes. Within the experimental resolution, it is possible to observe two librational peaks in favourable cases. A definite assignment of these peaks could not be made even by comparison with other available data. Vibrational frequencies in K2C2O4 · H2O, Ba(ClO3)2 · H2O, and BeSO4 · 4H2O have been obtained from crystal energy consideration. From their comparison with the observed frequencies it may be seen that the nearest‐neighbour hydrogen bond is the dominant interaction for the calculations of the librational frequencies in these salts.