Raman scattering factors

Theoretically determined Raman intensities are given in terms of Raman scattering factors Sk for mode k,... 

The first temi results in Rayleigh scattering which is at the same frequency as the exciting radiation. The second temi describes Raman scattering. There will be scattered light at (Vq - and (Vq -i- v ), that is at sum and difference frequencies of the excitation field and the vibrational frequency. Since a. x is about a factor of 10 smaller than a, it is necessary to have a very efficient method for dispersing the scattered light. 

One of the best available texts describing the principles of Raman scattering from crystals. Includes factor group calculations, polarization measurements, force constant calculations, and many other aspects of crystal physics. 

Since Raman scattered light intensity is very weak, of the order of 10-7 of the excitation line intensity, more powerful laser sources than the He-Ne laser are often needed. The Ar+ laser emits various lines in the region from 457.9 nm to 514.5 nm, of which the most powerful lines (typically — 700 mW) at 488.0 nm (blue) and 514.5 nm (green) are preferred. Furthermore, two other factors which favor the use of the high frequency excitation lines are the peak sensitivity of the photomultipliers in this blue-green region (Fig. 8) and the fourth power Raman intensity law... 

Ren et al. reported a method to prepare a gold tip with a tip apex radius of 30 nm reproducibly [27]. They observed the TERS of a Malachite Green isothiocyanate (MGITC) monolayer on an Au(lll) surface and obtained an enhancement factor of about 1.6 X 10, by using the relation, q= /TERs/lRRs=g /l focus where q is the net increase in the signal. Iters snd rrs the signal intensities for TERS and RRS (resonance Raman scattering), respectively is the TERS enhancement (gis the field enhancement), a denotes the radius of the enhanced field, and Rfocus the radius of the laser focus. 

The use of near-IR-laser excited FT-SERS eliminates the disturbing fluorescence of impurities found with visible excitation, and provides SERS enhancement factors that are about 20 times larger than those found for excitation at 514.5nm [792]. For a strong Raman scatterer (fluorene), a typical detection limit of 500 ng is found for a 3-mm diameter spot. For weak scatterers, the detection limits may be in the high- xg region, which means that some compromise between chromatographic... 

Six comments are appropriate at this point. Firstly, it is the experience of the reviewer that chemically-similar compounds with very similar infrared and Raman spectra in factor-group split regions are isomorphous. This method is probably at least as reliable as X-ray powder methods when there is a significant change in scattering factors between the two compounds studied (e.g. bromo-derivatives of... 

In resonant Raman spectroscopy, the frequency of the incident beam is resonant with the energy difference between two real electronic levels and so the efficiency can be enhanced by a factor of 10 . However, to observe resonant Raman scattering it is necessary to prevent the possible overlap with the more efficient emission spectra. Thus, Raman experiments are usually realized under nonresonant illumination, so that the Raman spectrum cannot be masked by fluorescence. 

Fister, J. C., Ill, and J.M. Harris. 1996. Factor analysis of transient Raman scattering data to resolve spectra of ground- and excited-state species. In Computer assisted analytical spectroscopy. Ed. S. D. Brown. New York Wiley. 

Field enhancement factors observed in Raman scattering from molecules adsorbed on nanosurfaces are even larger. The intensity of Stokes component in Raman scattering is proportional to the square of dipole momentum on that frequency [61] ... 

Radioactive label, 330 Raman diffusion, 184 Raman scattering, 227 Ratio fluorimeter, 228 Rayleigh scattering, 226 Real mean, 385 Red-shift, 196 Reference electrode, 347 Reflectron, 298 Refractive index detector, 59 Relative response factor, 78 Relative standard deviation, 387 Reliability, 389 Resolving power, 282 Response factor, 77 Restrictor, 98 Retardation factor, 88 Retention factor, 14 Retention index, 41 Retention time, 7 Retention volume, 14 RP-18, 53 RSD, 387 Ruhemann, 112... 

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