I. Natkaniec

Ab initio calculations and INS measurements of phonons and molecular vibrations in a model peptide compound – urea

Abstract Density functional theory (DFT) methods, as implemented in the V asp code, are used to calculate the inelastic neutron scattering (INS) spectrum of urea, which has been measured on the T osca spectrometer at ISIS, UK and the NERA-PR spectrometer at Dubna, Russia. Urea presents an extended network of bifurcated hydrogen bonds resulting in significant dispersion of the vibrational excitations, both for external and internal modes. The small mass of the molecule also results in intense multiphonon contributions to the spectral profile. Recent, successful applications of DFT in molecular spectroscopy are extended here using the P honon code to include dispersion and multiphonon contributions to the INS spectrum. Thus the whole spectral profile is calculated with only the crystal structure as input. The accuracy of the calculated normal modes is demonstrated for protonated and deuterated urea.

Neutron spectroscopy of MnH0.86, NiH1.05, PdH0.99 and harmonic behaviour of their optical phonons

Abstract Inelastic neutron scattering spectra from manganese, nickel and palladium hydrides synthesized under a high pressure of gaseous hydrogen have been measured in the energy region of 0–500 meV. The positions and intensities of the peaks in the higher energy parts of the spectra are well described by a contribution from the multiphonon neutron scattering in the harmonic approximation.

Crystal field splitting observed in RNi2 compounds (R = Pr, Nd, Tb, Er, Ho, Tm) by means of inelastic neutron scattering

Abstract Results of inelastic neutron scattering from a series of the cubic RNi 2 (R = Pr, Nd, Tb, Ho, Er and Tm) compounds are presented. From the spectra for the paramagnetic phase the crystalline electric field parameters A 4 and A 6 were determined. The values of A 4 are positive and of the same order of magnitude, whereas the A 6 -values have more scatter. The line widths for the Pr, Tb and Tm compounds are substantially larger than for the others. An interpretation of the spectra from the ordered samples has been attempted by taking into account magnetic dipole and quadrupolar interaction of the 4f-electrons in the mean field approximation.

The IINS spectroscopy of amino acids: l- and dl-valine

Abstract Results of the inelastic incoherent neutron scattering (IINS) study on normal and N-deuterated l and dl -valine at pulsed reactor IBR-2 are reported. l -Valine spectra show additional bands as compared with dl -valine due to the difference in the respective molecular conformation. Both in l - and dl -valine, lines corresponding to out-of-plane γ(N-H ··· O) hydrogen bond vibrations are observed at 279, 505, 513 cm−1 and 276, 559, 592 cm−1, respectively.

Parameters of the NERA spectrometer for cold and thermal moderators of the IBR-2 pulsed reactor

The inverted geometry time-of-flight spectrometer NERA designed for simultaneous investigation of elastic and inelastic neutron scattering was constructed on a 100 meter long flight path of the IBR-2 reactor at JINR, Dubna, Russia. Spectrometer parameters were optimized for the thermal neutron spectrum of a water moderator at 330 K. Recently, a new type of cold neutron source operating at 30 K was installed in the sector of six horizontal channels. The cold source in combination with the water moderator allows one to effectively use incident neutrons in wide range of wavelengths.

The IINS spectroscopy of amino acids: l-isoleucine

Abstract Results of inelastic incoherent neutron scattering (IINS) supplemented by infrared (IR) and Raman scattering studies on normal and N -deuterated l -isoleucine in the energy transfer up to 800 cm −1 are reported. The IINS spectra of l -isoleucine show additional bands as compared to the spectra obtained by optical spectroscopic methods. In both, normal and d 3 - l -isoleucine, extra bands correspond to out-of-plane γ (N–H⋯O) (518, 505, 250 cm −1 ) and γ (N–DO⋯O) (362 cm −1 ) hydrogen bond vibrations. Methyl and carboxyl groups vibrations are observed at 219, 228, 250, 281 cm −1 and 175, 543, 686, 749 cm −1 respectively.

Neutron scattering studies on structural phase transitions of superionic conductor Cs HSO4

Abstract The results of neutron diffraction (ND) and inelastic incoherent neutron scattering (IINS) studies on phase transitions and vibrational spectra in superionic conductor CsHSO4 at pulsed reactor IBR-2 are reported. It is shown that in the temperature range 123–420 K there are three phases (III, II, I) in CsHSO4 crystal and only two phases (II, I) in partly deuterated Cs(D0.7H0.3)SO4 crystal. The unit cell parameters in monoclinic phase II by ND on single crystal are determined. A considerable change in IINS spectra in superionic phase I says for a disorded state of protons in the lattice in this phase.

The dynamical pattern of the 2-aminopyrazine-3-carboxylic acid molecule by inelastic and incoherent neutron scattering, Raman spectroscopy and ab initio calculations

Abstract Inelastic and incoherent neutron scattering and Raman spectra were measured for 3-amino-2-carboxylic acid. Geometries were optimised and harmonic frequencies calculated at both semiempirical (AM1, MNDO, PM3) and ab initio Hartree–Fock (HF) levels using the 3-21G, 6-31G, 6-31G**, 6-311G and 6-311** basis sets. The observed frequencies were assigned using the HF/6-311G results.

Dynamics of hydrogen-bonded water networks under high pressure: Neutron scattering and computer simulation

Abstract Molecular dynamics simulation of proton-ordered high pressure ice modifications II and IX was performed. Dynamics of both isotope varieties, H2O and D2O, was simulated. Rectangular simulation box of ice II contained 576 and that of ice IX 768 molecules. The average kinetic energy corresponded to 82 and 201 K for ice II and to 87 and 203 K for ice IX. One-phonon densities of states were calculated via Fourier transformation of velocity autocorrelation functions and compared with those found experimentally from inelastic incoherent neutron scattering. This characteristic was calculated for all the molecules, as well as for the molecules of a particular crystallographic type. Both simulated ice modifications contain molecules of two different structural types. Dynamic characteristics of molecules of different types are slightly different. Splitting of the librational peak at about 60–70meV observed in the ice II experimental spectrum is mainly due to such difference. In the case of ice II simulated spectra reproduce experimental ones quite reasonably in the whole range of energies, while in the case of ice IX agreement with the experiment is worse.

Inelastic neutron scattering study of proton dynamics in Ca(OH)2 at 20 K

Abstract Inelastic neutron scattering (INS) spectra of Ca(OH) 2 at 20 K are presented from 30 to 4000 cm −1 for a powder sample, from 30 to 12000 cm −1 for an oriented single-crystal. INS band splitting due to the lattice density-of-states is observed. Polarization effects reveal the orientation of atomic displacements for each mode and a new band assignment scheme is proposed. For the single-crystal, the v OH mode and overtones are observed. This oscillator shows only moderate anharmonicity. Spectrum simulation reveals that INS spectral intensities are not consistent with simple normal coordinates and harmonic force-fields for Ca(OH) 2 entities. A new dynamical model is proposed, including anharmonic terms mixing the vibrational states of the OH and lattice modes. Previous assignment schemes proposed on the basis of infrared and Raman data are reconsidered. The structure of the OH stretching mode observed in the infrared is related to the lattice modes density-of-states.