Electro-absorption spectroscopy

Hagler, T. W., Pakbaz, K., and Heeger, A. J., Polarized electro-absorption spectroscopy of a soluble derivative of poly(p-phenylenevinylene) oriented by gel processing in polyethylene polarization anisotropy, the off-axis dipole moment, and excited state delocalization, Phys. Rev. B, 49, 10968-10975 (1994). 

Since the photophoretic force depends on the electromagnetic absorption efficiency Q y , which is sensitive to wavelength, photophoretic force measurements can be used as a tool to study absorption spectroscopy. This was first recognized by Pope et al. (1979), who showed that the spectrum of the photophoretic force on a 10 foa diameter perylene crystallite agrees with the optical spectrum. This was accomplished by suspending a perylene particle in a Millikan chamber with electro-optic feedback control and measuring the photophoretic force as a function of the wavelength of the laser illumination. Improvements on the technique and additional data were obtained by Arnold and Amani (1980), and Arnold et al. (1980) provided further details of their photophoretic spectrometer. A photophoretic spectrum of a crystallite of cadmium sulfide reported by Arnold and Amani is presented in Fig. 11. 

Photoluminescence excitation spectroscopy (PLE) is generally used to identify the excited-state structure in quantum wells. For GalnN/GaN quantum wells, Im et al [14] used PLE to study single wells of various widths. Similarly to the results from absorption, electro-absorption, and electroreflectance measurements, a large Stokes shift of the onset of the PLE spectrum with respect to the dominating photoluminescence peak was observed at low temperature [14]. 

Electro-absorption (EA) spectroscopy, where optical absorption is observed under the application of an electric field to the sample, is another method that can distinguish between localised and inter-band excitations. The electric field produces a Stark shift of allowed optical absorptions and renders forbidden transitions allowed by mixing the wavefunctions of the excited states. Excitons show a quadratic Stark (Kerr) effect with a spectral profile that is the first derivative of the absorption spectrum for localised (Frenkel) excitons and the second derivative for charge transfer excitons, i.e. 

It has been suggested that the first step of reaction (6) may be the formation of a carboxylic species COOHads. Carboxyl radicals have indeed been observed by Zhu et al." for potentials lower than 0.65 V using Fourier Transform infrared Reflectance Absorption Spectroscopy with the Attenuated Total Reflection mode (ATR-FTtR). Moreover Anderson et al." made numerical simulation which indicated that the formation of an adsorbed carboxylic species was energetically more favorable. Here, it has to be noted that the electro-oxidation of CO being a stracture sensitive reaction (sensitive to the superficial stracture symmehy" and to the presence of surface defects) this species can be used to study the activity of a catalyst but also as a molecular probe to characterize the catalytic surface. ... 

AAS Atomic Absorption Spectroscopy Atomize (flame, electro, thermal, etc.) Light e.g., glow discharge Absorption spectrum - - Concentralion ol atomic species (quantitative, using standards) 1,2... 

Both charge isomers have a relative molecular mass of32,000 daltons. The isomerism is attributed to the different isoelectric points of the proteins No differences were found in metal content, antigenicity, electron paramagnetic resonance and electron absorption spectroscopy Holo- and apo-superoxide dismutase, which have electro-... 

The third example is the reflection measurement at a rotating disk electrode (RDE). Scherson and his coworkers have developed near-normal incidence UV-visible reflection-absorption spectroscopy at RDEs [50-52]. Both (AR/R)dc and (AR/R)er have been measured under hydrodynamic conditions. The use of an RDE enables them to quantitatively control the diffusion layer concentration profile of the solution phase species, especially the species generated electro-... 

Chemical and electro-oxidation of this spiro molecule were studied using electrochemical methods and UV-visible absorption spectroscopy [11,36]. The hep-tamer segments were oxidized sequentially by using FeCls to produce the mono radical cation, the bis-(radical cation), the radical cation/dication and the bis-(dication) respectively (Scheme 14.13). 

Recently, a somewhat different synthetic approach has been reported. Halcrow et al. (215) synthesized a series of five-coordinate copper(II) complexes comprising a tridentate tris(pyrazolyl)borate ligand and a bidentate phenol derivative. Neutral complexes [Cun(TpPh)(bidentate phenolate)] were synthesized and structurally characterized [Tpph] = hydrido-tris(3-phenylpyrazol-l-yl)borate. The species [Cun(TpPh)(2-hydroxy-5-methyl-3-methylsulfanylbenzaldehydato)] can electro-chemically be converted to the (phenoxyl)copper(II) monocation, which has been characterized in solution by UV-vis spectroscopy. It displays two intense absorption maxima at 907 nm (e = 1.2 x 103 M 1 cm-1), and 1037 (1.1 x 103 M l cm-1), resembling in this respect the radical cofactor in GO (Fig. 7). 

Transient terahertz spectroscopy Time-resolved terahertz (THz) spectroscopy (TRTS) has been used to measure the transient photoconductivity of injected electrons in dye-sensitised titanium oxide with subpicosecond time resolution (Beard et al, 2002 Turner et al, 2002). Terahertz probes cover the far-infrared (10-600 cm or 0.3-20 THz) region of the spectrum and measure frequency-dependent photoconductivity. The sample is excited by an ultrafast optical pulse to initiate electron injection and subsequently probed with a THz pulse. In many THz detection schemes, the time-dependent electric field 6 f) of the THz probe pulse is measured by free-space electro-optic sampling (Beard et al, 2002). Both the amplitude and the phase of the electric field can be determined, from which the complex conductivity of the injected electrons can be obtained. Fitting the complex conductivity allows the determination of carrier concentration and mobility. The time evolution of these quantities can be determined by varying the delay time between the optical pump and THz probe pulses. The advantage of this technique is that it provides detailed information on the dynamics of the injected electrons in the semiconductor and complements the time-resolved fluorescence and transient absorption techniques, which often focus on the dynamics of the adsorbates. A similar technique, time-resolved microwave conductivity, has been used to study injection kinetics in dye-sensitised nanocrystalline thin films (Fessenden and Kamat, 1995). However, its time resolution is limited to longer than 1 ns. 

Note Key CL = chemiluminescent EC = electro-chemical FID = flame ionization detector GC = gas chromatograph HC = hydrocarbons IR = nondispersive infrared LA = line absorption Para. = paramagnetic RS = Raman spectroscopy. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, are discussed in articles the tides of which, for the most part, are descriptive of the analytical method. For example, both infrared (ir) and near infrared analysis (nira) are described in Infrared and raman SPECTROSCOPY. Nudear magnetic resonance (nmr) and electron spin resonance (esr) are discussed in Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed in Spectroscopy (see also Chemh.itmtnescence Electro-analytical technique Immunoassay ZvIass spectrometry Microscopy Microwave technology. Plasma technology and X-ray technology). 

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