Neutron diffraction study experimental method

Kossiakoff (1985) pointed out that the most useful attribute of neutron diffraction studies of proteins (compared with X-ray diffraction) is their ability to locate hydrogen (or deuterium) experimentally. Recent advances in apparatus and data acquisition mean that this method will become increasingly valuable in the study of a-lactalbumin and lysozyme, especially in the location of water molecules and the dynamics of these proteins. An example of a recent application is that by Lehmann et al. (1985). 

A variety of methods can now be used to probe intermolecular interactions. The structural information on intermolecular interactions obtained from X-ray and neutron diffraction studies can be compared with gas-phase experimental data from pure rotational or rotation-vibrational spectra [1] and the energies obtained from ab initio molecular orbital calculations. It is found that each of these methods generally gives essentially the same result. While most X-ray diffraction studies are on crystals of small molecules, comparisons with the lower-resolution results of protein crystallographic studies give information on interactions in an environment that consists of about 50 % water by volume [8]. 

During the last two decades, studies on ion solvation and electrolyte solutions have made remarkable progress by the interplay of experiments and theories. Experimentally, X-ray and neutron diffraction methods and sophisticated EXAFS, IR, Raman, NMR and dielectric relaxation spectroscopies have been used successfully to obtain structural and/or dynamic information about ion-solvent and ion-ion interactions. Theoretically, microscopic or molecular approaches to the study of ion solvation and electrolyte solutions were made by Monte Carlo and molecular dynamics calculations/simulations, as well as by improved statistical mechanics treatments. Some topics that are essential to this book, are included in this chapter. For more details of recent progress, see Ref. [1]. 

However the sample is prepared, we measure 13C spectra of one or more adsorbates on the catalyst, and then need to interpret the spectra to deduce the structure of adsorption complexes or reactive intermediates formed on the catalyst. In many cases the complexes and intermediates formed are unusual and exotic species for which the interpretation of the spectra may be far less than routine. This is where ab initio chemical shift calculations are essential. In diffraction methods, such as x-ray or neutron diffraction, one can more-or-less easily invert the experimental data to yield molecular structure. There is no straightforward relationship between chemical shift data and structure theoretical calculations provide the bridge between experiment and theory. In a typical study, we model the adsorbates on clusters that represent catalyst active sites, using experience and chemical intuition to create our initial structures. 

The magnetic oxide compound CUB2O4 hass attracted much attention because of its nature, such as successive phase transitions, the soliton lattice, etc. The properties have been studied by several experimental methods, involving the magnetic susceptibility [1], the specific heat [2], ESR [3, 4],, uSR [5], neutron diffraction [6, 7], nonlinear optics [8] etc. In these investigations, it has been found that the material undergoes... 

Nitromethane, CH -NOf. The equilibrium structure of singlet nitromethane has been studied at several levels of theory [3,60,64-71]. Two conformations are possible for nitromethane, staggered (Is) and eclipsed (le), but the eclipsed form has been characterized as a transition structure at MP2/6-31G with an imaginary frequency of 30 cm 1 [3]. Rotation around the H3C-NO2 bond occurs essentially without barrier the estimated value is only 0.01 kcal/mol. This is in accordance with a microwave study, which reports a C-N rotation barrier of only 6 cal/mol [72,73]. The C-N bond length of nitromethane has been estimated with X-ray single crystal diffraction [74], neutron diffraction [46,75], microwave spectroscopy [72,73], MP2/6-31G [3], and B3LYP/6-31+G [71] at respectively 1.449, 1.486, 1.489, 1.485, and 1.491 A, showing that the theoretical estimates compare very well with those determined by experimental methods. The experimentally reported vibrational frequencies of nitromethane... 

The experimental investigations of the role of water in clay minerals are often devoted to the study of properties and the structure of water molecules using several experimental techniques like neutron and X-ray diffraction, incoherent neutron scattering, IR, NMR and ESR spectroscopy, and dielectric relaxation. Among these methods, neutron diffraction, neutron scattering and NMR techniques have become the most powerful techniques in the study of this phenomenon. 

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