Experimental characterization techniques vibrational spectroscopy

Good summaries of accepted experimental techniques can be found in the references that are cited for individual radionuclides in the sections below. Nitsche (1991) provides a useful general summary of the principles and techniques of solubility studies. A large number of techniques have been used to characterize the aqueous speciation of radionuclides. These include poten-tiometric, optical absorbance, and vibrational spectroscopy. Silva and Nitsche (1995) summarize the use of conventional optical absorption and laser-based photothermal spectroscopy for detection and characterization of solution species and provide an extensive citation list. A recent review of the uses of Raman and infrared spectroscopy to distinguish various uranyl hydroxy complexes is given by Runde et al. (2002b). 

Correlations of in situ and ex situ observations. The characterization methods of surface science have already been established within an electrochemical context, because they can provide structural definition of fine distance scales as well as atomic composition of a surface and, sometimes, vibrational spectroscopy of adsorbates. These ex situ methods normally involve transfer of an electrode from the electrochemical environment to ultrahigh vacuum, and the degree to which they provide accurate information about structure and composition in situ is continuously debated. Additional work is needed to clarify the effect of emersion of samples and their transfer to ex situ measurement environments. The most appropriate experimental course requires observations by techniques that can be employed in both environments. Vibrational spectroscopy, ellipsometry, radiochemical measurements, and x-ray methods seem appropriate to the task. Once techniques suited to this problem are established, emphasis should be placed on the refinement of transfer methods so that the possibilities for surface reconstruction and other alterations in interfacial character are minimized. 

The search for faster screening methods capable of characterizing propolis samples of different geographic origins and composition has lead to the use of direct insertion mass sp>ectrometric fingerprinting techniques (ESf-MS and EASI-MS), which has proven to be a fast and robust method for propoHs characterization (Sawaya et al., 2011), although this analytical approach can only detect compoimds that ionize under the experimental conditions. Similarly, Fourier transform infrared vibrational spectroscopy (FITR) has also demonstrated to be valuable to chemically characterize complex matrices such as propolis (Wu et al, 2008). 

From an experimental standpoint, information on the dye binding modes at the semiconductor/dye interface, are conventionally accessed by vibrational spectroscopy [Fourier Transform InfraRed (FT-IR) spectroscopy and Surface-Enhanced Raman Spectroscopy (SERS)] [228-237]. These techniques can provide structural details about the adsorption modes as well as information on the relative orientation of the molecules anchored onto the oxide surface. Photoelectron Spectroscopy (PES) has also been successfully employed to characterize the dye/oxide interface for a series of organic dyes [238-242]. The analysis of the PES spectra yields information on the molecular and electronic structures at the interface, along with basic indications of the dye coverage and of the distance of selected atoms from the... 

The atoms in a molecule vibrate about their equilibrium positions, and the following description of molecular vibrations sets the stage for a discussion of vibrational spectroscopy (Chapter 12), an important experimental technique for the structural characterization of biological molecules. 

Among various spectroscopic techniques, IR and RS are commonly utilized in experimental science. IR-active modes and RS-active modes are known to be mutually exclusive in centrosymmetric molecules because these optical processes are realized as one-photon and two-photon transitions, respectively (Fig. 5.1). It is important to obtain full vibrational information when characterizing materials. Therefore, a combined use of both methods should be helpful for understanding their chemical structures. However, this is practically difficult due to relatively low energies of infrared photons, IR spectroscopy sometimes faces problems, e.g., in situ observation in IR-opaque aqueous solution. RS spectroscopy often suffers with... 

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