A full conformational study of solid-state anhydrous adenine is reported, using vibrational spectroscopy techniques coupled to DFT calculations, for the isolated molecule and the solid. In both cases, the N9H-amino tautomer was found to be the predominant species, followed by the N7H-amino form. An excellent agreement was achieved between experiment and theory, both for wavenumbers and intensities (without the need for scaling). A complete spectral assignment was performed, since all vibrational spectroscopic techniques were available to this study -FTIR, Raman and INS - allowing us to detect and interpret even the lowest frequency vibrational bands, not previously accessed. The quantum mechanical calculations presently carried out represent the highest theoretical level applied so far to the study of nucleobases.

Chromone and two carboxylic derivatives - chromone-2-carboxylic acid (2CA) and chromone-3-carboxylic acid (3CA) - were investigated as to their conformational preferences by vibrational spectroscopy - Raman, FTIR and INS - combined to density functional theory and plane-wave calculations. INS experiments allowed to clearly detect intramolecular hydrogen-type close contacts in these systems. A natural bond orbital (NBO) analysis was performed, including calculation of the second-order perturbation energies (E-(2)) and orbital occupancies, to provide theoretical evidence of the stabilisation due to the pi(i)* -> pi(j)* donor-acceptor interaction. A complete assignment of the vibrational spectra was achieved for all compounds, allowing us to determine their most stable conformers and establish their H-bonding profile. 3CA was shown to display a particularly strong intramolecular H-bond, which can explain its singular conformational behaviour and abnormally high pK(a) value. (c) 2012 Elsevier B.V. All rights reserved.

Structural and dynamical investigations on concentrated aqueous solutions of aluminium chloride and bromide in liquid and glassy states have been performed by means of Raman and inelastic neutron scattering spectroscopy and by x-ray diffraction. Inelastic neutron scattering results for solutions of beryllium chloride in a glassy state are compared with the results for the aluminium cation solutions. Isotopic changes on going from H2O to D2O of the Raman spectra assigned to vibrations of water molecules in the cation hydration shells are discussed. Inelastic neutron scattering data complement and corroborate the Raman spectral study. Further structural information is obtained from x-ray diffraction experiments, and its interpretation is supported by calculations based on ad hoc molecular models. The existence of a liquid-type quasi-close packing is suggested for concentrated aqueous solutions of aluminium halides, in agreement with previous studies.

The role that model compounds can play in understanding the vibrational eigenvectors of molecules is discussed. Assigning the spectra of model compounds is of particular importance and the individual-scaling approach, that has been used with isolated molecule ab-initio calculations, is outlined. Special emphasis is given to recent work on assigning the spectra of three 5–6 heterobicyclic systems; indole, benzimidazole and isatin.

We have investigated the vibrational spectrum of the dihydrogen complex [W(CO)3(n2-H2)(P{isopropyl}3)2] with particular emphasis on the inelastic neutron scattering spectrum. Previous work treated the motion of the dihydrogen ligand as either the rotational transitions of dihydrogen in a deep attractive well or as the modes of a dihydrogen complex. We have shown that neither model on its own can account for the inelastic neutron scattering spectrum. The rotational model requires the addition of vibrations and the vibrational model, as calculated by density functional theory, requires the addition of a split ground state. We have also shown that there is significant mechanical coupling of the dihydrogen modes to those of the other ligands, especially the carbonyls. Simulation of the method used in the literature, shows that the most important result, the location of the torsional mode, is validated, but that the method is not reliable for higher energy modes. Assignments for the carbonyl modes and come of the skeletal modes are also given. The implications of the vibrational coupling for the use of the dihydrogen complexes as model compounds for surface species are considered.

We have used low energy inelastic neutron scattering spectroscopy to examine the tunnelling spectroscopy of the ammonium ion in the (NH4)(0.02)RbxK0.98-xI system. The concentration of different species were varied as x increased, this was followed systematically and the first consistent assignment scheme for these features is given. Differences were also found for the relaxation rate of the spin temperature inversions that could be generated in these species. At a critical concentration-about x = 0.04 mole fraction-the relaxation rates of the species changed dramatically.

The VESUVIO spectrometer at the ISIS pulsed neutron source performs inelastic neutron scattering at high-energy and wave vector transfers, employing gold and uranium resonant foils. A factor of two improvement in the instrumental resolution has been achieved by making use of the double filter difference method. Experimental results are presented for measurements on polycrystalline Pb, which indicate that accurate measurements of single-particle momentum distribution n(p) in quantum fluids are now possible at eV energy transfers.

Epithermal neutrons are unique probes for deep inelastic neutron scattering (DINS) at high-energy and high-momentum transfer and inelastic neutron scattering (INS) at high-energy and low-wave vector transfers. In the latter case the kinematic range has recently been revisited given that the high values of initial and final wave vectors achievable in a scattering process coupled to small scattering angles allow to access a so far unexplored region in q,ω, i.e ω>1eV and q<10 Å−1. In order to exploit DINS and INS in the high-energy and low-momentum range, a very low angle detector (VLAD) bank will be delivered within the e.VERDI Project together with a novel bank at intermediate scattering angles. The former will provide a new tool for investigating high-energy excitations in magnetic systems and semiconductors. The VLAD bank will be constructed following the concept of a resonance detector (RD) spectrometer, recently revised for DINS experiments in the range 1–100eV.This is a more promising approach in terms of efficiency and signal-to-noise ratio compared to standard neutron counting techniques at eV energies. Results from two devices, cadmium zinc telluride (CZT) solid-state detectors and YAlO3 perovskite (YAP) scintillators used in RD configurations, will be presented.

Issues raised by Fillaux et al. [Chem. Phys. Lett., this issue] regarding the Letter by Wilson et al. [Chem. Phys. Lett. 381 (2003) 102] are considered, and the aims of the modelling undertaken by Wilson et al. on the potassium hydrogen maleate system reiterated, in particular the fact that the equilibrium PES is discussed in Wilson et al. (2003).

A study of the biogenic polyamines spermidine and spermine, as well as of the diamines H2N(CH2),NH2 (n = 2-10 and n = 12), was carried out by both inelastic neutron scattering (INS) and Raman spectroscopies, for both their undeuterated and N-deuterated forms. Ab initio density functional theory (DFT) methods were also used, to obtain the calculated vibrational spectra of those molecules. A thorough vibrational analysis was performed, leading to the assignment of the solid-state spectra, both Raman and INS, of the polyamines studied, comprising all their longitudinal acoustic modes (LAM's).

The inelastic neutron scattering spectra of the n-alkanes, obtained at ca. 25 K, have been examined in the frequency region below 260 cm−1. Assignments of the transverse acoustic modes (TAMs) of pentane to dodecane out to wavevectors, κ, of about 0.6 are presented. These emerge from a general scheme, which is broadly applicable to all alkanes but inconsistent with single molecule ab initio calculations (because of the mode mixing introduced by the presence of external forces). The external vibrational spectra of the n-alkanes were reported for the first time and shown to have an n-even, n-odd, dependence, in agreement with the variations reported for their crystal structures. However, the demonstration of a similar n-even, n-odd, alternation in the methyl torsion frequencies must be understood in terms of the internal, and not the external, forces.

Inelastic incoherent neutron scattering (IINS) spectra were obtained at 10 K for normal and deuterated L-serine. The geometry of L-serine molecule was optimized for the zwitterion form using ab initio HF, MP2 and DFT (B3LYP) levels with 6-31G* and 6-311 + +G4** basis sets. The theoretical frequencies of normal and d4-L-serine were compared with IINS spectra. Normal coordinate analysis and band assignments based on ab initio calculations and experimental data were presented. IINS frequencies due to the out-of-plane gamma(N-H...O) hydrogen bond motions were observed and identified.

The forward and backward scattering parts (phase II) of the new neutron spectrometer, TOSCA, replacing the old TFXA and TOSCA (phase I), have been successfully installed at the ISIS pulsed neutron source. The results show a significant enhancement in the counting rate due to the larger detector area. The improved resolution (to 1.5–3% of the energy transfer) as compared with the previous instruments (TXFA: 2.5–3.5%; TOSCA-I: 2–3.5%) has been achieved by increasing the primary flight path from 12 m to 17 m. A chopper has been added in order to avoid neutron frame overlap and to reduce the fast neutron background. Additional diffraction capability will be installed in the near future. An example of the high resolution that is routinely available is provided by the spectrum of potassium hydrogen phtalate at 20 K.

Inelastic incoherent neutron scattering spectra (IINS) were obtained for normal and deuterated L-threonine. Raman and infrared spectra were also recorded. Geometries were optimized for the zwitterion form using ab initio Hartree-Fock (HF) levels with 6-31G*, 6-311G*, 6-311G** and 6-311 + + G** basis sets. Force fields and normal modes were calculated and used as basis for an assignment of the spectral features.

The back-scattering part (phase I) of the new incoherent inelastic neutron spectrometer, TOSCA, replacing the old TFXA, has been successfully installed at the ISIS pulsed neutron spallation source. The results, owing to the much larger detector area, show a significant enhancement of the counting rate and an improvement of the resolution. In spring 2000, the forward scattering bank (phase II) will be completed and, during the final installation, the whole instrument will be moved from the present 12 m primary flight path to 17 m. This will result in a large improvement of the overall resolution (from 2–3% to 1–1.5% of the energy transfer). A chopper will be added in order to avoid neutron frame overlap and to reduce the fast neutron background. In addition, TOSCA will have a diffraction capability.

The calibration of a time-focused spectrometer for the analysis of inelastically back-scattered neutrons is discussed. By comparison with a reference spectrum, a non linear system of the kinetic equations for neutrons is obtained and the calibration process is outlined. This provides a deeper understanding of the question of expected inaccuracies on the measured spectra. In particular, the effect on the parameters of a possible misassignment of the reference spectrum features is examined in detail. A suitable molecular crystal (2,5 diiodothiophene) is identified as the recommended calibrant. Using different transitions from the spectrum of this calibrant the inaccuracies introduced by misassignment are assessed.

New hydrofullerite was synthesized from C-60 fullerite treated in hydrogen atmosphere at 30 Kbar and 620 K during 24 hours The inelastic neutron scattering (MS) spectra of the quenched as-prepared and annealed samples showed that the as-prepared hydrofullerite consisted of C60Hn (n approximate to 32) molecules with molecular hydrogen dissolved onto interstitial sites. The MS and optic spectra of annealed hydrofullerite show features which are characteristic of polymeric fullerites or of endohedrally trapped H-2 molecules. The low-energy behavior of the MS spectra gives a hint that some part of hydrogen can be trapped in the atomic form.

The inelastic neutron scattering (ZNS) spectra from 16 to 4000 cm(-1) are presented for lamellar-like manganese dioxides at 30 K: delta -MnO2 and chemically modified Bi-delta -MnO2 at various reduction degrees (Bi-delta -MnO1.96, Bi-delta -MnO1.88, Bi-delta -MnO1.78, Bi-delta -MnO1.70, and Bi-delta -MnO1.51). Three different types of protons are distinguished: water-like entities at 540 cm(-1), oxonium-like entities at 815 cm(-1), and free protonic entities giving a continuum with constant intensity. The nonreduced samples contain equimolecular mixtures of water-lace and oxonium-like entities, and there is no visible modification of the spectra attributable to the Bi entities. As the reduction degree increases, the band intensity at 540 cm(-1) decreases and that at 815 cm(-1) increases. Free protons are virtually unaffected. Even for the most reduced sample, there is no evidence for any feature specific to protons inserted in the [MnO6] layers. TRIO processes can be distinguished: the removal of water molecules by the solvent on the one hand and the protonation of water-like entities on the other. (C) 2000 The Electrochemical Society. S0013-4651(00)01-079-X. All rights reserved.