Neutron vibrational spectroscopy

Although the question of orientation order does not arise, these results for argon monolayers illustrate several features of neutron vibrational spectroscopy. Well-defined excitations can be observed at somewhat lower energy transfers than accessible with optical and electron energy-loss spectroscopies. Typical energy resolution in the scans of Fig. 2 is 0.3 meV (2.4 cm"1). The capability of obtaining inelastic spectra at constant non-zero Q is also not present in these other spectroscopies. However, scattered intensities are relatively low. Counting times in Fig. 2 were -30 minutes per point. 

C. A model system for neutron vibrational spectroscopy of adsorbed molecules monolayer butane on graphite. In this section we concentrate on a particular system, monolayer n-butane adsorbed on graphite, for which a considerable effort has been made to analyze the inelastic neutron spectra for the orientation of the adsorbed molecule and the forces bonding it to the substrate (10,19,20). By treating one system in greater detail, we can better illustrate the capabilities and limitations of the technique. 

Although not exhaustive, the above summary of experiments with hydrogen chemisorbed on transition-metals serves to illustrate how neutron vibrational spectroscopy is performed with catalytic substrates and the methods used to analyze the inelastic neutron spectra. In concluding this section we note that the technique can be extended to supported catalysts such as in recent experiments with hydrogen adsorbed on both MoS and alumina supported MoSp (38). Also, as another indication of the variety of systems which can be studied, we note earlier experiments with ethylene (39) and acetylene (40) adsorbed on silver exchanged 13X zeolites. "Tn this work, deuteration of the molecules was helpful in identifying the surface vibratory modes on these ionic substrates of greater complexity. 

In this chapter we have presented and reviewed the extensive body of work that neutron vibrational spectroscopy applied to catalysis represents. It is one of the largest, most important and influential bodies of neutron work to appear in the literature and much of the original work remains of considerable interest. This is partly because catalyst experiments are difficult to perform and require considerable commitment of neutron time and other resources. 

R.R. Cavanagh, R.D. Kelley JJ. Rush (1982). J. Chem. Phys., 77, 1540-1547. Neutron vibrational spectroscopy of hydrogen and deuterium on Raney nickel. 

C. Karmonik, T.J. Udovic, R.L. Paul, J.J. Rush, K. Lind R. Hemplemann (1998). Solid State. Ionics, 109, 207-211. Observation of the dopant effects on hydrogen modes in SrCeo.95Mo.o5 H ,03.8 by neutron vibrational spectroscopy. 

There is an enormous body of work on quasielastic neutron scattering from polymers [1,2]. There is a smaller literature on neutron vibrational spectroscopy of polymers but this has had a significant impact on the characterisation of these materials. Crystalline or semi-crystalline polymers are the most important class of polymers commercially. The most-studied and technologically most important of these is polyethylene and this will be considered in some depth and we will highlight the use of the n-alkanes as model compounds ( 10.1.2). We will then see how these concepts can be transferred to polypropylene ( 10.1.3), nylon ( 10.1.4), and conducting polymers ( 10.1.5). Non-crystalline polymers ( 10.2) have been much-less studied by INS. As examples, we will consider polydimethylsiloxane ( 10.2.1) and advanced composites ( 10.2.2). 

R. Essmann, H. Jacobs J. Tomkinson (1993). J. Alloys Cmpds., 191, 131-134. Neutron vibrational spectroscopy of imide ions (NH ) in bariumimide (BaNH). 

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. 

NEUTRON VIBRATIONAL SPECTROSCOPY OF DISORDERED METAL-HYDROGEN SYSTEMS... 

A review is presented of some recent applications of neutron vibrational spectroscopy to the study of disordered metal-hydrogen systems. The examples discussed cover a range of systems from simple dilute solutions in bcc or fee metals to amorphous alloy hydrides. It is shown that neutron inelastic scattering studies of the vibrational density of states provide a powerful and sensitive probe of the local potentials and bonding sites of hydrogen in metals and often reveal critical information on the novel microscopic physical properties and behavior of disordered metals-hydrogen systems, including those influenced by interstitial or substitutional defects. 

A recent application of this isotope dilution neutron spectroscopy concerns H atoms chemisorbed on the surface of Pt. Fig. 3 shows the vibrational spectra of 100 H and of 90 D + 10 H on Pt. Due to a high incoherent neutron scattering cross section, H atoms on substrates with large surface areas can be investigated by means of neutron vibrational spectroscopy / whereas D atoms are much more difficult to probe. So for the H isotope mixture coverage in Fig. 3 only the H defect mode is visible and, in order to apply Eq. 11, the pure 100 H spectrum was scaled down by /T to derive the deuteride density of states, assuming harmonic forces. 

The aim of this review was to give a flavor of neutron vibrational spectroscopy and its application to disordered metal-hydrogen systems as well as to demonstrate that such studies yield important microscopic information which cannot be obtained any other way. 

Whether the probing particle is a photon, an electron, an atom or a neutron, vibrational spectroscopy may be divided into the following groups (see e.g. [16])... 

Fig. 42.10 Neutron vibration spectroscopy of H2O-DNA at 20 K at different concentrations, a Number of percentage indicates grams of water per 100 g dry DNA. b Starting from bottomcurve is in order of lyophilized DNA, 25, 50, 75, 100, 150, 200 g of water per 100 g DNA (Reprinted with permission from [70])...

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