UV-Visible Techniques

The phenomenon of fluorescence has been synonymous with ultraviolet (UV) and visible spectroscopy rather than near-infrared (near-IR) spectroscopy from the beginning of the subject. This fact is evidenced in definitive texts which also provide useful background information for this volume (see, e.g., Refs. 1-6). Consequently, our understanding of the many molecular phenomena which can be studied with fluorescence techniques, e.g., excimer formation, energy transfer, diffusion, and rotation, is based on measurements made in the UV/visible. Historically, this emphasis was undoubtedly due to the spectral response of the eye and the availability of suitable sources and detectors for the UV/visible in contrast to the lack of equivalent instrumentation for the IR. Nevertheless, there are a few notable exceptions to the prevalence of UV/visible techniques in fluorescence such as the near-IR study of chlorophyll(7) and singlet oxygen,<8) which have been ongoing for some years. 

NMR and UV-visible techniques have been used in the characterization of intermediates in the [Fe (edta)]" -promoted decomposition of hydrogen peroxide7 Fe complexes of edta, nta, and dtpa react with FISOs by an inner-sphere one-electron transfer mechanism with transient production of S04, in contrast to Cu, which reacts by an outer-sphere mechanism to give S04 and hydroxy radicalsFe -edta redox properties are relevant to Fe /Cu /H202 systems. ... 

In Situ Techniques 3.2.5.2.1 Optical Techniques UV-visible Techniques... 

UV-visible techniques were proven usefiil, they are not suitable for identifying adsorbates or orientation of adsorbates. This type of information could be provided by the various versions of vibrational spectroscopy. 

I will present hae the studies of KsMoCle and CrCls -LiCl-KCl electrolytes whae both electrochemical and UV-Visible techniques are used. 

Whilst UV-visible techniques have proved extremely useful, they unfortunately lack molecular specificity. This means that they are not suitable for identifying adsorbates or studying adsorbate orientation and local environment. This type of information is best provided by vibrational spectroscopy, and therefore a considerable effort has been expended in developing vibrational spectroscopies that can be used in situ in an electrochemical cell. This effort is beginning to pay off, and techniques based on both infrared spectroscopy and Raman scattering spectroscopy are being increasingly used. 

Most of the existing work concerning the structure of organic anions in solution has been performed with carbanions, enolates and fenoxi-des2y ketyls and semiquinone derivatives, such studies were based principally on ESR, NMR and UV-visible techniques, and in particular the latter have been limited to very dilute solutions in a narrow range of concentrations, due to the very high molar extinction coefficient of the anions. 

Beden B 1995 On the use of in situ UV-visible and infrared spectroscopic techniques for studying corrosion products and corrosion inhibitors Mater. Sc/. Forum 192-4 277... 

Most of the experimental information concerning copolymer microstructure has been obtained by physical methods based on modern instrumental methods. Techniques such as ultraviolet (UV), visible, and infrared (IR) spectroscopy, NMR spectroscopy, and mass spectroscopy have all been used to good advantage in this type of research. Advances in instrumentation and computer interfacing combine to make these physical methods particularly suitable to answer the question we pose With what frequency do particular sequences of repeat units occur in a copolymer. 

In a few instances the technique of magnetic circular dichroism (MCD) spectroscopy has been used to corroborate assignments based on UV-visible spectroscopy. For example, the assignment of the intense 360 nm band for [S,N,Y to a r (2e") r (2a2") (HOMO LUMO) excitation has been confirmed by the measurement of the MCD spectrum of The MCD spectrum of [S4N3] indicates that each of the... 

These early results have since been confirmed and extended by a vast and still growing body of research. All of the contemporary spectroscopic techniques (ir, uv, visible, nmr, esr) have been brought to bear on the problem, and further confirmation has come from cryoscopic and conductometric studies. The early confusion that resulted from the coexistence of both donor-acceptor or non-covalently-bonded complexes) has been clarified. This research has been extensively reviewed10,13-15 and will not be detailed here. 

Infrared spectroelectrochemical methods, particularly those based on Fourier transform infrared (FTIR) spectroscopy can provide structural information that UV-visible absorbance techniques do not. FTIR spectroelectrochemistry has thus been fruitful in the characterization of reactions occurring on electrode surfaces. The technique requires very thin cells to overcome solvent absorption problems. 

Visible and UV spectrophotometric techniques are most convenient for studying the polymer and various oxidation states of plutonium. The spectra of the plutonium states and the procedure for resolution of the concentrations were previously described (9 ). Changes in the relative concentrations of the oxidation states and of the polymer generally are determined from corresponding changes in the spectra and a comparison of the changes to standard spectra of the various states. These techniques have been used exclusively for studying the photochemistry of aqueous plutonium. 

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

The optical absorption spectra of sulfonyl radicals have been measured by using modulation spectroscopy s, flash photolysis and pulse radiolysis s techniques. These spectra show broad absorption bands in the 280-600 nm region, with well-defined maxima at ca. 340 nm. All the available data are summarized in Table 3. Multiple Scattering X, calculations s successfully reproduce the experimental UV-visible spectra of MeSO 2 and PhSO 2 radicals, indicating that the most important transition observed in this region is due to transfer of electrons from the lone pair orbitals of the oxygen atoms to... 

The development of hydrodynamic techniques which allow the direct measurement of interfacial fluxes and interfacial concentrations is likely to be a key trend of future work in this area. Suitable detectors for local interfacial or near-interfacial measurements include spectroscopic probes, such as total internal reflection fluorometry [88-90], surface second-harmonic generation [91], probe beam deflection [92], and spatially resolved UV-visible absorption spectroscopy [93]. Additionally, building on the ideas in MEMED, submicrometer or nanometer scale electrodes may prove to be relatively noninvasive probes of interfacial concentrations in other hydrodynamic systems. The construction and application of electrodes of this size is now becoming more widespread and general [94-96]. 

Electronic spectroscopy, often referred to as UV/visible spectroscopy, is a useful instrumental technique for characterising the colours of dyes and pigments. These spectra may be obtained from appropriate samples either in transmission (absorption) or reflection mode. UY/visible absorption spectra of dyes in solution, such as that illustrated in Figure 2.3, provide important information to enable relationships between the colour and the molecular structure of the dyes to be developed. 

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