Raman measurements

Loring R F and Mukamel S 1985 Selectivity in coherent transient Raman measurements of vibrational dephasing in liquids J. Chem. Phys. 83 2116-28... 

Figure C3.5.11. IR-Raman measurements of vibrational energy flow tlirough acetonitrile in a neat liquid at 300 K, adapted from [41], An ultrashort mid-IR pulse pumps the C-H stretch, which decays in 3 ps. Only 1% of the energy is transferred to the C N stretch, which has an 80 ps lifetime. Most of the energy is transferred to the C-H bend plus about four quanta of C-C=N bend. The daughter C-H bend vibration relaxes by exciting the C-C stretch. The build-up of energy in the C-C=N bend mirrors the build-up of energy in the bath, which continues for about 250 ps after C-H stretch pumping.

Fig. 4.1. Variation of NO2+ ion concentration with the concentration of mixed acid (nitric sulphuric, i mole i mole) inorganic solvents (a) in sulpholan (6)in aceticacid (c) in nitromethane. Curves (a) and (6) were determined by Raman measurements using the 1400 cm band while curve (c) was derived from infra-red measurements on the 237s cm band. Unity on the NO2+ concentration scale was determined to be 5-6 molar ( 2S 8 weight %). (From Olah et...

Raman measurements [INFRARED TECHNOLOGY AND RAMAN SPECTHOSCOPY - RAMAN SPECTHOSCOPY] (Vol 14)... 

Maximum information is obtained by making Raman measurements on oriented, transparent single crystals. The essentials of the experiment are sketched in Figure 3. The crystal is aligned with the crystallographic axes parallel to a laboratory coordinate system defined by the directions of the laser beam and the scattered beam. A useful shorthand for describing the orientational relations (the Porto notation) is illustrated in Figure 3 as z(xz) y. The first symbol is the direction of the laser beam the second symbol is the polarization direction of the laser beam the third symbol is the polarization direction of the scattered beam and the fourth symbol is the direction of the scattered beam, all with respect to the laboratory coordinate system. 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

The Raman measurements provide values directly for P)mn, the coefficients of the Legendre expansion related to coordinates axes chosen with respect to the principal axes of the differential polarizability tensor, hence the superscript r. The coefficients Pimn for the orientation of the units of structure must then be obtained by further calculation from the P)mn. 

It can readily be appreciated that in the absence of any knowledge regarding the differential polarizability tensor, it is a difficult exercise to obtain precise information from the Raman measurements. However, if r is known, Equations (19) are six linear simultaneous Equations in the six quantities (ot2I0N0) 1, P)0o> P220) PIoo> P420 and... 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

It is important from a practical viewpoint to predict the shear viscosity of mixtures from those of pure melts. For alkali nitrate melts, a linear dependence has been found between the reorientational line width obtained by Raman measurements and the ratio of temperature divided by shear viscosity.For NO3 ions, the depolarized Raman scattering from 1050cm" total stretching vibrational mode (Al) has a contribution to the line width L, which is caused by the reorientational relaxation time of the Csv axis of this ion. The Stokes-Einstein-Debye(SED) relation establishes a relation between the shear viscosity r of a melt and the relaxation time for the reorientation of a particle immersed in it ... 

Figure 2.9 Spectra of a single adenine nanocrystal, (a) TERS spectrum, (b) ordinal SERS spectrum, and (c) ordinary near-infrared (NIR) Raman spectra. For the SERS measurement, a silver island film was used. For the NIR Raman measurement, i thick sample of adenine was used with a 1 h exposure.

Time-domain Raman measurement of molecular submonolayers by time-resolved reflection spectroscopy. /. Phys. Chem. B, 108, 1525-1528. 

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

Spatially Integrated Resonance Raman Measurements of Macular Pigment.90... 

Raman measurements of skin carotenoid levels could be used as an indirect, rapid optical method to assess fruit and vegetable consumption in large populations. 

SPATIALLY INTEGRATED RESONANCE RAMAN MEASUREMENTS OF MACULAR PIGMENT... 

Bergeson SD, Peatross JB, Eyring NY, Fralick JF, Stevenson DN, and Ferguson SB (2008), Resonance Raman measurements of carotenoids using light emitting diodes, J. Biomed. Opt. 13 044026-1-044026-6. 

Bernstein PS, Zhao DY, Wintch SW, Ermakov IV, and Gellermann W (2002), Resonance Raman measurement of macular carotenoids in normal subjects and in age-related macular degeneration patients, Ophthalmology 109 1780-1787. 

Gellermann W, Ermakov IV, Ermakova MR, McClane RW, Zhao DY, and Bernstein PS (2002a), In vivo resonant Raman measurement of macular carotenoid pigments in the young and the aging human retina, J. Opt. Soc. Am. A 19 1172-1186. 

It has been important to determine if the neoxanthin distortion signature could be detected during the nonphotochemical quenching in vivo. Resonance Raman measurements on leaves and chlo-roplasts of various Arabidopsis mutants have revealed a small increase in the 950 cm 1 region. The relationship between the amplitude of this transition and the amount of NPQ suggests that the LHCII aggregation may be the sole cause of the protective chlorophyll fluorescence quenching in vivo (Ruban et al., 2007). 

Raman sensors can be used for all three physical states. It possible to measure gases, though at the expense of sensitivity due to the lower sample density, liquids and solids of different forms and shapes. Basically any Raman active substance could be detected, also in aqueous solution, provided substance and the sample matrix permit Raman measurements (fluorescence problem, absorption,. ..) and the analyte concentrations are sufficiently high. 

In Figure 3 is shown the experimental set-up used for micro-Raman measurements. 

For Raman measurements, the collected spectra were compared directly with the Raman spectra database of pigments compiled by the Chemical Department of University College of London. 

A stress-induced alignment can also be detected in Raman experiments. The sensitivity of a vibration to the polarization of the incident and scattered light in a Raman experiment is determined by the polarizability tensor for the vibration. Even in the absence of polarization information, IR absorption or Raman measurements made in the presence of stress can be used to detect a preferential alignment of a defect by the effect the alignment has on the relative intensities of the stress-split-components of a vibrational band. 

The interpretation of the stress dependent intensities is that the stress raises the energy of those B—H configurations with their axis along the direction of stress. The H has sufficient thermal energy at 100 K to reorient (Fig. 20b) the different orientations are populated according to their (stress-dependent) Boltzmann factors. Because the H can move at the measurement temperature (100 K) on the time scale of a Raman measurement (a few minutes) Herrero and Stutzmann (1988b) were able to estimate an upper limit for the barrier for H-motion. These authors assumed that the rate limiting step for H motion obeys first order kinetics and obtained Eb < 0.3 eV. 

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