John F. C. Turner

The effect of apolar solutes on water structure: Alcohols and tetraalkylammonium ions

Neutron diffraction with hydrogen/deuterium isotope substitution on the solvent water hydrogens is used to investigate changes in water structure around the apolar groups on alcohols and tetraalkylammonium ions at room temperature. The HH and HX correlations (where X is a nonsubstituted atom) are calculated for the following solutes in water: ethanol (5 mol%), tertiary butanol (3 mol%), tetrapropylammonium bromide (2.4 mol%), and tetrabutylammonium bromide (1.7 mol%). The correlation functions suggest that the water structure in all four systems is very similar to bulk water. There is no evidence of structural enhancement in going from pure water to water in the alcohol–water mixtures. There is a small but probably significant increase in structure in the tetraalkylammonium bromide solutions compared to both pure water and the alcohol–water mixtures. There is very little measurable difference between the two alcohol–water mixtures or the two tetraalkylammonium bromide solutions in terms of water structure...

Synthesis of carbon nanotubes containing metal oxides and metals of the d-block and f-block transition metals and related studies

The filling of carbon nanotubes with metals and metal oxidesvia one- and two-step processes is presented. Both molten media and wet chemistry solution methods have been used to introduce foreign materials into the hollow nanotube cavities. Chemical reactions inside the tubes have been carried out, including the reduction of encapsulated materials to the metals. The nature of the crystalline filling has been found to be highly dependent on the techniques used. Wet chemical methods tend to result in filling which consists of discrete crystallites, whereas molten media methods tend to give long, continuous single crystals.

A neutron-diffraction study of tetramethylammonium chloride in aqueous solution

Neutron diffraction with isotope substitution of nitrogen, chlorine and hydrogen nuclei is used to investigate the hydration region of both ions and the possibility of ion pairing in aqueous solutions of tetramethylammonium chloride (TMACl) at 0·5 m, 1·0 m and approximately 2·0 m concentration. The use of a maximum-entropy method to calculate the radial distribution functions is discussed. The H-H correlation function for the water in the 1·0 m solution is measured and compared with that for pure water. The nitrogen-substitution results are also compared with a hard-sphere model calculation. The results show that the TMA hydration is apolar rather than ionic, and is consistent with a disordered water-cage structure, while the water in the hydration sphere does not appear to be more ordered than in bulk water. There is no significant change in the hydration structure measured at the different concentrations, although at the highest concentration there may be evidence of the close approach of the anion and ...

Water structure in aqueous solutions of tetramethylammonium chloride

Neutron diffraction with hydrogen/deuterium isotope substitution is used to investigate the water structure and the solute distribution in aqueous solutions of tetramethylammonium chloride ((CH3)4NCl) between 2·0 and 8·0m concentrations at room temperature. The hydrogen-hydrogen (HH) pair correlation functions for the water indicate that the hydrogen-bonding geometry is not significantly changed over the concentration range compared to pure water, although the number of hydrogen bonds to nearest-neighbour water molecules decreases with increase in anion concentration. The results show no evidence of increased water structure compared to pure water in either the nearest-neighbour or the longer distance range.

Transition metal-carbonyl, -hydrido and -η-cyclopentadienyl derivatives of the fullerene C60

Monoadduct derivatives of the fullerence C60, namely [Fe(CO)4(η2-C60)], [Mo(η-C5H4R)2(η2-C60)](R = H, Bun), [Ta(η2-C5)](η2-C60)] and Rh (ph(Ph3P)2(CO)(η2-C60)H], are described.

Isotope quantum effects in water around the freezing point

We have measured the difference in electronic structure factors between liquid H(2)O and D(2)O at temperatures of 268 and 273 K with high energy x-ray diffraction. These are compared to our previously published data measured from 279 to 318 K. We find that the total structural isotope effect increases by a factor of 3.5 over the entire range, as the temperature is decreased. Structural isochoric temperature differential and isothermal density differential functions have been used to compare these data to a thermodynamic model based upon a simple offset in the state function. The model works well in describing the magnitude of the structural differences above approximately 310 K, but fails at lower temperatures. The experimental results are discussed in light of several quantum molecular dynamics simulations and are in good qualitative agreement with recent temperature dependent, rotationally quantized rigid molecule simulations.

Solute-solute correlations in aqueous solutions of tetramethylammonium chloride

Neutron diffraction with hydrogen/deuterium isotope substitution on the methyl group hydrogen atoms of the solute is used to investigate the distribution of the tetramethylammonium (TMA) ion, (CH3)4N+, in aqueous solution of 4·0 molal tetramethylammonium chloride at room temperature. The centre-centre correlation function for TMA ions is calculated from the HH correlation function for the solute by deconvolution of a spherical form factor representing the distribution of methyl hydrogen atoms. The centre-centre function shows a broad distribution of TMA … TMA distances, but indicates that close contacts occur frequently. This suggests that the charge interaction of TMA is not important in determining the distribution and that the TMA ion behaves more like an apolar solute.

Quantum state-resolved energy redistribution in gas ensembles containing highly excited N2.

A computational model is used to quantify the evolution of quantum state populations as highly vibrationally excited (14)N(2) ((14)N(2)∗) equilibrates in various bath gases. Multicollision energy disposal follows general principles established in related single collision processes. Thus when state-to-state routes permit, maximum amounts of energy are deposited into partner species by direct vibration-to-vibration (V-V) exchange. When these pathways are absent, e.g., when Ar is the bath species, relaxation is very slow and multistaged. Conversely, in a bath of v = 0 (14)N(2) molecules, 16 vibrational quanta (Δv = ± 8) are resonantly exchanged from (v;j) = (8;10) with vibrational equilibration so rapid that rotation and translation still lag far behind after 1000 collisions. Near-resonant V-V exchange dominates the initial phase when (15)N(2) forms the bath gas and although some rotational warming occurs, vibrational modes remain decoupled from, and significantly hotter than, the low heat capacity modes. These forms of behavior seem likely to characterize excited and bath species that have closely similar vibration and rotation constants. More generic in nature is (14)N(2) in O(2) or in a mixture that closely resembles air. Here, asymmetric V-V exchange is a dominant early feature in ensemble evolution but energy differences in the key vibration and rotation quanta lead to V-V energy defects that are compensated for by the low energy modes. This results in much more rapid ensemble equilibration, generally within 400-500 collisions, when O(2) is present even as a minor constituent. Our results are in good general agreement with those obtained from experimental studies of N(2) plasmas both in terms of modal temperatures and initial (first collision cycle) cross-sections.

Structure and dynamics of methyl groups in the deuterated microporous organic–inorganic hybrid, aluminium methylphosphonate-β

Neutron powder diffraction at 4.6 K and 2 H NMR spectroscopy over the range 100-400 K have been used to examine the structure and rotational dynamics of CD groups pointing into the unidimensional channels of the b-polymorph of the 3 . hybrid organicrinorganic microporous solid aluminium methylphosphonate, Al CD PO . The methyl groups rotate 23 3 3 rapidly at all temperatures studied in the NMR experiments, with a correlation time in the fast limit of ; 2 = 10 y13 s and with an activation energy of ; 10 kJ mol y1 . Extrapolation to 4.6 K indicates that the groups will be stationary and this is confirmed by the neutron diffraction experiment, where the lowest-energy configurations of the methylphosphonate groups are all found to have the methyl deuterons staggered with respect to the phosphonate oxygens. q 1999 Elsevier Science B.V. All rights reserved.

The use of synchrotron x rays to exploit the Warren–Mavel fluorescence detection technique in studies of disordered systems

Although the early structural studies of liquids and amorphous systems used x‐ray diffraction, the advent of high flux reactor sources led to neutron diffraction becoming the preferred technique. There are several advantages: high scattering vector information is not form factor limited and, where isotopes exist, the variation in scattering length allows more detailed structural information to be extracted in many cases. However, the development of synchrotron radiation sources has generated renewed interest in x‐ray measurements. High intensity is available at wavelengths short enough to give reasonable access to the high scattering vector region and, in theory, the tunability can be used to maximize anomalous scattering effects and so allow element specific scattering to be recorded. Another use of the tunability is for largely removing the Compton scattering which can often dominate the total scattered intensity and which contains no structural information. This technique requires a choice of incident ...