Neutron spectroscopic applications

Neutron scattering techniques are increasingly being used to study the structure and dynamics of molecules adsorbed in nanoporous materials. The most prominent example is neutron diffraction, which is complementary to X-ray diffraction to solve structural problems in zeolites and other microporous materials [1]. While the use of powder neutron diffraction is well established in the zeolite community, the spectroscopic applications of neutron scattering are less familiar. However, the constant amelioration of the neutron instrumentation and of the theoretical models provides unprecedented insights into the dynamics of the framework and of adsorbed molecules, at the atomic and... 

Eckert J and Kearley GJ eds (1992) Spectroscopic applications of inelastic neutron scattering theory and practice. Spectrochimica Acta 48A 269-478. 

Europium has been identified spectroscopically in the sun and certain stars. Seventeen isotopes are now recognized. Europium isotopes are good neutron absorbers and are being studied for use in nuclear control applications. 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

If high temperatures eventually lead to an almost equal population of the ground and excited states of spectroscopically active structure elements, their absorption and emission may be quite weak, particularly if relaxation processes between these states are slow. The spectroscopic methods covered in Table 16-1 are numerous and not equally suited for the study of solid state kinetics. The number of methods increases considerably if we include particle radiation (electrons, neutrons, protons, atoms, or ions). We note that the output radiation is not necessarily of the same type as the input radiation (e.g., in photoelectron spectroscopy). Therefore, we have to restrict this discussion to some relevant methods and examples which demonstrate the applicability of in-situ spectroscopy to kinetic investigations at high temperature. Let us begin with nuclear spectroscopies in which nuclear energy levels are probed. Later we will turn to those methods in which electronic states are involved (e.g., UV, VIS, and IR spectroscopies). 

A good example for testing the applicability of our approach is the 13-decay of the odd-proton (Z=37) nucleus Rb to the odd-neutron (N=61) daughter Sr. As was shown in IPFE84], even from a rather time-consuming spectroscopic investigation of 9 Rb decay at OSTIS, resulting in g.s. band properties considerably improved over those reported in an earlier... 

Our approach to this problem involves a detailed mechanistic study of model systems, in order to identify the (electro)chemical parameters and the physicochemical processes of importance. This approach takes advantage of one of the major developments in electrochemical science over the last two decades, namely the simultaneous application of /ton-electrochemical techniques to study interfaces maintained under electrochemical control [3-5]. In general terms, spectroscopic methods have provided insight into the detailed structure at a variety of levels, from atomic to morphological, of surface-bound films. Other in situ methods, such as ellipsometry [6], neutron reflectivity [7] and the electrochemical quartz crystal microbalance (EQCM) [8-10], have provided insight into the overall penetration of mobile species (ions, solvent and other small molecules) into polymer films, along with spatial distributions of these mobile species and of the polymer itself. Of these techniques, the one upon which we rely directly here is the EQCM, whose operation and capability we now briefly review. 

Each spectroscopic method has a characteristic application. For example, flame photometry is still applicable to the direct determination of Ca and Sr, and to the determination of Li, Rb, Cs and Ba after preconcentration with ion-exchange resin. Fluorimetry provides better sensitivities for Al, Be, Ga and U, although it suffers from severe interference effects. Emission spectrometry, X-ray fluorescence spectrometry and neutron activation analysis allow multielement analysis of solid samples with pretty good sensitivity and precision, and have commonly been applied to the analysis of marine organisms and sediments. Recently, inductively-coupled plasma (ICP)... 

Inelastic neutron scattering (INS) is a spectroscopic technique in which neutrons are used to probe the dynamics of atoms and molecules in solids and liquids. This book is the first, since the late 1960s. to cover the principles and applications of INS as a vibrational-.spectroscopic technique. It provides a hands-on account of the use of INS. concentrating on how neutron vibrational spectroscopy can be employed to obtain chemical information on a range of materials that are of interest to chemists, biologists, materials scientists, surface scientists and catalyst researchers. This is an accessible and comprehensive single-volume in imary text and reference source. 

This volume in the Series on Neutron Techniques and Applications is the first account in book form since the late 1960s of the principles and applications of inelastic neutron scattering (INS) as a vibrational spectroscopic technique. Our aim has been to provide a hands-on account of inelastic neutron scattering concentrating on how neutron scattering can be used to obtain vibrational spectroscopic and bonding information on a range of materials. 

The application of neutron scattering to understanding the role of hydrogen in solids has been described in various general reviews [4,5]. Specific applications to intermetallic compounds are described by Richter et al. [6]. Its use in vibrational spectroscopic studies in chemistry, biology, materials science and catalysis are described by Mitchell et al. [7]. For a review of the basic properties of metal-hydrogen systems, we would refer the reader to the book by Fukai [8]. 

The tetragonal RE, Y, and Sc orthophosphates in particular have been widely used as host media for a variety of solid state chemical, spectroscopic, magnetic resonance, neutron and other studies of rare-earth and actinide impurities. These materials have proved to be ideal hosts for the incorporation of other rare-earth dopants (e.g., Er-doped Lu(P04) for microlaser studies). Doped orthophosphates with desired levels of dopants are desirable for both basic investigations and applications. Unfortunately, there are apparently no available quantitative data on the segregation coefficients for the rare earths in the tetragonal orthophosphates. 

Naturally, a fundamental requirement is the determination of the structure of the molecular sieves imder study (cf. Voliune 2) through techniques such as X-ray diffraction, neutron scattering, electron microscopy and so on. However, a remarkably broad variety of methods and tools are at our disposal for characterizing the physical and chemical properties of molecular sieves. Voliune 4 of the series Molecular Sieves - Science and Technology focuses on the most widely used spectroscopic techniques. Thereby, the contributions to this voliune not only review important applications of these techniques, but also comprise, to a greater or lesser extent, the basic principles of the methods, aspects of instrumentation, experimental handling, spectra evaluation and simulation, and, finally, employing spectroscopies in situ for the elucidation of processes with molecular sieves, e.g. synthesis, modification, adsorption, diffusion, and catalysis. 

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