Raman scattering experimental work

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

Under constant experimental conditions, the number of Raman scattered photons is proportional to analyte concentration. Quantitative methods can be developed with simple peak height measurements.5 Just as with IR calibrations, multiple components in complex mixtures can be quantified if a distinct wavelength for each component can be identified. When isolated bands are not readily apparent, advanced multivariate statistical tools (chemometrics) like partial least squares (PLS) can help. These work by identifying all of the wavelengths correlated to, or systematically changing with, the levels of a component. Raman spectra can also be correlated to other properties, such as stress in semiconductors, polymer crystallinity, and particle size because these parameters are reflected in the local molecular environment. 

Time resolved coherent anti-Stokes Raman spectroscopy of condensed matter has been recently extended to the femtosecond domain allowing direct and detailed studies of the fast relaxation processes of molecular vibrations in liquids. The vibrational phase relaxation (dephasing) is a fundamental physical process of molecular dynamics and has attracted considerable attention. Both experimental and theoretical studies have been performed to understand microscopic processes of vibrational dephasing. Developments in ultrafast coherent spectroscopy enables one now to obtain direct time-domain information on molecular vibrational dynamics. Femtosecond time-resolved coherent anti-Stokes Raman scattering measuring systems have been constructed (see Sec. 3.6.2.2.3) with an overall time resolution of less than 100 fs (10 s). Pioneering work has been per-... 

Since surface-enchanced Raman scattering spectroscopy is still a relatively new technique, its theory and experimental conditions have not yet been completed. Much experimental and theoretical work will have to be undertaken to enable the data to be evaluated more precisely and more quantitatively. Only then will it be possible to assume that this technique might be ranked with other physical techniques suitable for structural studies such as normal solution Raman or nuclear magnetic resonance (NMR) spectrophotometry. The two latter techniques can provide information about the structure of molecules at the level of single atoms, but to carry out solution Raman or NMR spectrometry experiments relatively very high concentrations of the compound are needed. SERS or SERRS could be one way of overcoming this problem, which is particularly inconvenient in the case of analysis of most biomacromolecules by physical or physico-chemical techniques. 

The symmetry coordinates of all the zc modes in ice VIII have been analyzed experimentally using Raman S, infraredand neutron scattering techniques and theoretically The theoretical work contains diagrams of the vibrations for all of the symmetry coordinates in Table 1. 

These NCS experiments [Chatzidimitriou-Dreismann 1997 (a) Chatzidimi-triou-Dreismann 1999 Karlsson 1999], which were motivated by the theoretical work of C. A. Chatzidimitriou-Dreismann [Chatzidimitriou-Dreismann 1991 Chatzidimitriou-Dreismann 1997 (b)] on protonic quantum entanglement in condensed systems and by the results of a an earlier Raman experiment on liquid H O / D O mixtures [Chatzidimitriou-Dreismann 1995], were followed by a series of other experiments on liquid and solid organic materials [Chatzidimitriou-Dreismann 2000 (b) Chatzidimitriou-Dreismann 2001 Chatzidimitriou-Dreismann 2002 (a)], various metallic hydrides [Abdul-Redah 2000 Karlsson 2002 (b) Karlsson 2003 (b)], liquid hydrogen [Chatzidimitriou-Dreismann 2004 (b)] and among others an ionic solid [Abdul-Redah 2004] using the same experimental technique, i.e., neutron Compton scattering. All these experiments confirmed the anomalous results found earlier and also revealed certain new aspects of the considered effect. 

The feature of the all considered experimental methods is that they allow us to define the values of the molecular polarizabilify only at the equilibrium position of molecular nuclei. To obtain the dependencies of molecular polarizabilities on the mutual location of nuclei in a molecule, the Raman effect can be used The line intensities of Raman spectra depend on the values of polarizability derivatives with respect to the nuclei displacements. The first works to define the polarizability derivatives of molecules have appeared immediately after the creation of the theory of Raman light scattering (Placzek theory of polarizability) [17]. However, the experimental technique of pre-laser period could not obtain the high-quality results. Some experimental results of this period are summarized in [18]. Currently, these data have only a historical interest. Now, laser technologies allow to increase the measurement accuracy and, as a result, significantly improve and revise the pre-laser data. Nevertheless, up to day the experimental data on flie polarizability derivatives of molecules are fragmentary and do not give the impression of systematic studies of the polarizability of molecules as a function of the nuclei coordinates, even for diatomic molecules [19-39]. 

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