Dispersion probing

Three different approaches have been employed to observe radiation-induced kinetics on the picosecond timescale. The first, pulse-probe detection, is covered in this section. Section 3.3 discusses a related technique that uses temporally-dispersed probe beams to record a kinetic trace in a single shot. Einally, Sec. 3.4... 

Sm fle-shot radiolysis usin f a temporally-dispersed probe beam... 

When TRAMs are made on dispersed probes, tc will reflect the speed of rotation of the fluorophore [20,46,60,76], which can be related to the microviscosity of the medium. In the context of probing the structure of PMAA, the fluorescent dyes have been occluded in the hypercoiled conformation [46,60,76] allowing an estimate of the size of the rotating, solubilizing cluster to be derived from the resultant tc. Alternatively, if the fluorophore is covalently attached to the polyelectrolyte in the form of a label then, depending on its mode of attachment, information concerning motion of the chain ends [46,60,76], the backbone [26,88,112,113], and chain substituents [26,88] can be derived from tc. 

Victor K, Kavolius V, Bryant RG (2004) Magnetic relaxation dispersion probe. J Magn Reson 171 253-257... 

Kojima, S., Tsumura, M., Takeda, M.W. and Nishizawa, S. (2003) Far-infrared phonon-polariton dispersion probed by terahertz time-domain spectroscopy. Phys. Rev. B, 67, 035102(1)-035102(5). 

The resonance vector analysis has been used to explore all of the questions raised above on the fate of the polyad numbers in larger molecules, the most thoroughly investigated case so far probably being C2FI2- This molecule has been very extensively probed by absorption as well as stimulated emission pumping and dispersed fluorescence teclmiques [, 53, 70 and 71], the experimental spectra have been analysed in... 

Lee S-Y 1995 Wave-packet model of dynamic dispersed and integrated pump-probe signals in femtosecond transition state spectroscopy Femtosecond Chemistry ed J Manz and L Wdste (Heidelberg VCH)... 

Because x-rays are particularly penetrating, they are very usefiil in probing solids, but are not as well suited for the analysis of surfaces. X-ray diffraction (XRD) methods are nevertheless used routinely in the characterization of powders and of supported catalysts to extract infomration about the degree of crystallinity and the nature and crystallographic phases of oxides, nitrides and carbides [, ]. Particle size and dispersion data are often acquired with XRD as well. 

The prediction of drop sizes in liquid-liquid systems is difficult. Most of the studies have used very pure fluids as two of the immiscible liquids, and in industrial practice there almost always are other chemicals that are surface-active to some degree and make the pre-dic tion of absolute drop sizes veiy difficult. In addition, techniques to measure drop sizes in experimental studies have all types of experimental and interpretation variations and difficulties so that many of the equations and correlations in the literature give contradictoiy results under similar conditions. Experimental difficulties include dispersion and coalescence effects, difficulty of measuring ac tual drop size, the effect of visual or photographic studies on where in the tank you can make these obseiwations, and the difficulty of using probes that measure bubble size or bubble area by hght or other sample transmission techniques which are veiy sensitive to the concentration of the dispersed phase and often are used in veiy dilute solutions. 

An experimental problem is to obtain adequate dispersion of the particles before sedimentation analysis. For powders that are difficult to disperse the addition of dispersing agents is necessary, together with mtrasonic probing. It is essential to examine a saiTmle of the dispersion under a microscope to ensure that the sample is fully dispersed. 

Close examination of the weld under a low-power stereoscopic microscope revealed small openings (Fig. 15.6). Probing these sites with a pin revealed a large pit that had been covered by a thin skin of weld metal. These sites contained fibrous, metallic remnants (Fig. 15.7). Examination under a scanning electron microscope further revealed the fibrous character of the material (Fig. 15.2) and also the convoluted shapes of the individual fibers (Fig. 15.21). Energy-dispersive spectrographic analysis of this material revealed the compositions in Table 15.1. 

The analyst has two practical means of measuring the energy distribution of X rays emitted from the specimen energy-dispersive spectrometry and wavelength dispersive spectrometry. These two spectrometers are highly complementary the strengths of each compensate for the weaknesses of the other, and a well-equipped electron probe instrument will have both spectrometers. 

Let us now return to the question of solvolysis and how it relates to the stracture under stable-ion conditions. To relate the structural data to solvolysis conditions, the primary issues that must be considered are the extent of solvent participation in the transition state and the nature of solvation of the cationic intermediate. The extent of solvent participation has been probed by comparison of solvolysis characteristics in trifluoroacetic acid with the solvolysis in acetic acid. The exo endo reactivity ratio in trifluoroacetic acid is 1120 1, compared to 280 1 in acetic acid. Whereas the endo isomer shows solvent sensitivity typical of normal secondary tosylates, the exx> isomer reveals a reduced sensitivity. This indicates that the transition state for solvolysis of the exo isomer possesses a greater degree of charge dispersal, which would be consistent with a bridged structure. This fact, along with the rate enhancement of the exo isomer, indicates that the c participation commences prior to the transition state being attained, so that it can be concluded that bridging is a characteristic of the solvolysis intermediate, as well as of the stable-ion structure. ... 

The simplest mode of IGC is the infinite dilution mode , effected when the adsorbing species is present at very low concentration in a non-adsorbing carrier gas. Under such conditions, the adsorption may be assumed to be sub-monolayer, and if one assumes in addition that the surface is energetically homogeneous with respect to the adsorption (often an acceptable assumption for dispersion-force-only adsorbates), the isotherm will be linear (Henry s Law), i.e. the amount adsorbed will be linearly dependent on the partial saturation of the gas. The proportionality factor is the adsorption equilibrium constant, which is the ratio of the volume of gas adsorbed per unit area of solid to its relative saturation in the carrier. The quantity measured experimentally is the relative retention volume, Vn, for a gas sample injected into the column. It is the volume of carrier gas required to completely elute the sample, relative to the amount required to elute a non-adsorbing probe, i.e. 

Fig. 17. A schematic of the alkane line obtained by inverse gas chromatography (IGC) measurements. The relative retention volume of carrier gas required to elute a series of alkane probe gases is plotted against the molar area of the probe times the. square root of its surface tension. The slope of the plot is yielding the dispersion component of the surface energy of...

The technique of IGC may be employed to obtain acid-base information, as suggested by Schultz and Lavielle [99], by using acid and base probe gases on a solid for which the alkane line has already been obtained. If acid-base interaction is involved in the adsorption, the retention volume should be greater than that corresponding to the dispersion force interaction alone, which should be the same as that of the equivalent alkane , i.e. the hypothetical alkane for which the value... 

To find the most efficient selectors in the library, blue and red dye-labeled enantiomeric probe molecules 6 and 7 were prepared by linking pentafluorophenyl esters of L- and D-proline with Disperse Blue 3 and Disperse Red 1, respectively, through an isophthaloyl (shown in structures 6 and 7) or a succinyl moiety. Eor detection, a... 

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