Inelastic neutron scattering infrared absorption

Vibrations in molecules or in solid lattices are excited by the absorption of photons (infrared spectroscopy), or by the scattering of photons (Raman spectroscopy), electrons (electron energy loss spectroscopy) or neutrons (inelastic neutron scattering). If the vibration is excited by the interaction of the bond with a wave... 

Raman scattering Infrared absorption Inelastic harmonic light scattering (Hyper-Raman) Neutron inelastic scattering Stimulated Raman scattering... 

These are, with decreasing resolution on the time scale, the methods of infrared and Raman spectroscopy, dielectrical absorption and NMR spectroscopy, and inelastic neutron scattering. Thermodynamic properties depend on the long lifetime average structures, which are observed by X-ray and neutron scattering. For each of these methods, the descriptor structure has a different meaning. 

Figure 2.2-1 Observation of the excitation of a vibrational state in the electronic ground stale 5o, by a, infrared absorption b, Ramtin scattering c, inelastic neutron scattering d, fliiorescence.

Volume 50 of Advances in Catalysis, published in 2006, was the hrst of a set of three focused on physical characterization of solid catalysts in the functioning state. This volume is the second in the set. The hrst four chapters are devoted to vibrational spectroscopies, including Fourier transform infrared (Lamberti et al.), ultraviolet Raman (Stair), inelastic neutron scattering (Albers and Parker), and infrared-visible sum frequency generation and polarization-modulation infrared rehection absorption (Rupprechter). Additional chapters deal with electron paramagnetic resonance (EPR) (Bruckner) and Mossbauer spectroscopies (Millet) and oscillating microbalance catalytic reactors (Chen et al.). 

Adsorbed hydrogen on metal surfaces is of particular interest from both theoretical and experimental points of view. Vibrational spectroscopy data on hydrogen adsorbed from the gas phase have been obtained from IR reflection-absorption experiments as well as from electron energy loss spectroscopy and inelastic neutron scattering techniques [39-41]. In UHV, absorption bands for the M-H bond have been reported in the mid- and far-infrared regions [41, 42],... 

Besides thermal excitation of phonons, they can also be excited systematically by inelastic neutron scattering, by Raman scattering, by infrared absorption, by coup-Ung to optical transitions or by coupUng to charge carriers within the crystal. The first three of these methods can be apphed to determine the phonon frequencies or the entire dispersion relations S2(K) quantitatively. This will be treated in the following Sect 5.4. 

For the experimental determination of the phonon dispersion relations S2(K), inelastic neutron scattering is by far the most powerful method, but it also requires the most effort Important complements to this method are however Raman scattering of light and infrared absorption spectroscopy. In particular, Raman scattering permits a precise determination of the frequencies of the Raman-active optical phonons with wavevectors K 0. It is thus particularly well suited to the evaluation of pressure and temperature dependences, which are especially prominent in the case of the soft organic molecular crystals. 

Table 5.3 Frequencies and symmetries of the 9 optical phonons (Nos. 12-4) at the P point (K = 0) in a perdeuterated naphthalene crystal, N-dg. The experiments were carried out at different temperatures inelastic neutron scattering at T= 6 K [7], Raman scattering at T = 25 K [12], and infrared absorption atT= 1.5 K [13]...

Infrared spectroscopy (IR) Raman spectroscopy X-ray absorption spectrometry (XANES, EXAFS) Nuclear magnetic resonance (NMR) Inelastic neutron scattering (INS)... 

From the many available spectroscopic techniques, the most frequently employed to provide information at the microscopic level in the study of zeolites are. X-ray diffraction and Inelastic Neutron Scattering (INS), infrared (IR) or Raman absorption spectroscopy and mmltinuclear Solid State Nuclear Magnetic Resonance (NMR). 

This approximate expression is similar to the response function (5.138) which we wrote down by analogy with the expressions (5.136,137) for e(o)), except that the harmonic frequency o).(q) has been replaced by the pseudo-harmonic frequency o)-(q) and r.(q) has been replaced by r.(q). From the ex-perimental point of view, we see that o)j(q) and Fj(q) are to be determined from the measured positions and half-widths of the infrared absorption bands, the Raman lines, or the peaks of inelastic neutron scattering spectra. Examples of infrared experimental data are shown in Fig.5.14. The pseudoharmonic frequencies d).(q) defined by (5.144) should not be confused with... 

Patterson and Lynn [6] have reported a lattice dynamical study of the host lattice CsjSiFg based on neutron scattering, Raman, and infrared absorption measurements. Dispersion relations for phonons with energies less than 160 cm have been determined along three symmetry directions by coherent inelastic neutron scattering experiments. In Fig. 7 the photon dispersion results for Cs2SiFg are shown [6] in which the experimental data are represented by circles. The solid lines correspond to dispersion curves calculated with a rigid-ion, lattice dynamical model. 

Fig. 2.2-Ic illustrates a similar process, the inelastic scattering of neutrons. Irradiating molecules with mono-energetic neutrons produce scattered neutrons according to an energy balance equivalent to Eq. 2.2-1. While Raman scattering as well as infrared absorption of symmetric molecules obeys strict selection rules, which allow or forbid the activity of certain vibrations in these spectra, inelastic scattering of neutrons is not subject to such rules. It is not usually applied in analytical chemistry, but it is used to study lattice vibrations of crystals in solid-state physics and dynamics of liquids.

This chapter treats principally the vibrational spectra determined by infrared and Raman spectroscopy. The means used to assign infrared absorption bands are outlined. Also, the rationale for the selection of permitted absorption bands is described. The basis for the powerful technique of Fourier Transform Infrared (FTIR) is presented in Appendix 6A. Polyethylene is used to illustrate both band assignment and the application of selection rules because its simple chain structure and its commercial importance have made polyethylene the most thoroughly studied polymer. The techniques of nuclear magnetic resonance, neutron inelastic scattering and ultraviolet spectroscopy are briefly described. The areas of dielectric loss and dynamic mechanical loss are not presented in this chapter, but material on these techniques can be found in Chapters 5. 

The two techniques most commonly used to observe vibrational spectra are infrared (IR) and Raman spectroscopy, although other techniques such as neutron scattering [8] can also be employed. Methods for obtaining IR and Raman data are considered in section 4.3, and comprehensive reviews have been given elsewhere [9, 10]. The IR spectrum arises from the absorption of radiation the frequency of which is resonant with a vibrational transition, while the Raman effect results from inelastic scattering of photons to leave a molecule or crystal in a vibrationally excited state. The shift in frequency of the scattered photon corresponds to the frequency of the normal mode that has been excited. 

Almost all infrared absorptions arise from the transitions between the energy levels of molecular vibrations. In this sense, infrared absorption spectra, together with Raman spectra and neutron inelastic scattering spectra, constitute vibrational spectra. Infrared absorption spectra observed from gases are accompanied by fine structures due to the transitions associated with rotational energy levels. As a result, vibration-rotation spectra are observed from gaseous samples. In liquids and solids, free rotation of molecules... 

Fig. 2a-e. Polyethylene absorption spectra in the far infrared region (a) from Chantry and Chamberlain, Ref. [2] (f) from Fleming et al. Ret [17] (b) neutron inelastic scattering data (c) dielectric loss tangent vs. wave numter (d) calculated density of phonon states (e) dielectric loss angle tangent vs. log v. (Reproduced from Bur, Ref. [18])... 

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