Surface Raman polarization

The fact that some Raman-active frequencies became infrared-active on adsorption suggests that high electric fields on the silica surface induced polarization of the adsorbate with subsequent loss of symmetry of the molecule. This loss of symmetry would permit previously forbidden vibrations to appear. 

Id usually appears as a thin film on a glass surface, and until now we have not succeeded in obtaining a single crystal for the X-ray analysis. However, there are some reasons to speculate about its structure. For disilenes of the type RR Si=SiR R, photochemical cis-tram isomerization in solution was shown to occur [11], the trans isomer being predominant under equilibrium conditions. Of course, symmetrically substituted 1 crumot have real cis—trans isomers, but, by analogy, a similar equilibrium with predominance of a conformer, close to the tram one, seems likely in solution. This assumption is eonfirmed by Raman polarization measurements for a solution of 1 in hexane, because the selection mles observed for the conformer predominant in solution are consistent with C2h symmetry, that is, with a quasi-/ra s structure of this conformer [12]. As both the Raman and UV-Vis absorption and fluorescence spectra of solid Id are similar to those of 1 in hexane solution [1,12], we can suggest for Id also a quasi-/ra/is structure as shown in Fig. I. 

Ago H, Uehara N, Uceda K-1, Ohdo R, Nakamura K, Tsuji M. Synthesis of horizon-taUy-aUgned single-waUed carbon nanotubes with controllable density on sapphire surface and polarized Raman spectroscopy. Chem Phys Lett 2006 421 399—403. 

X. Huang et al., Cancer cells assemble and align gold nanorods conjugated to antibodies to produce highly enhanced, sharp, and polarized surface Raman spectra a potential cancer diagnostic marker. Nano Letters, 7(6), 1591-1597 (2007). 

However, some polymeric samples contain crystallites or voids comparable in size to the visible wavelengths of the laser. These crystallites or voids scramble the incident laser polarization and thereby prevent any useful measurement of depolarization ratios. Some error in Raman polarization measurements arises because the incident light and Raman scattered light are multiply reflected at the surface of the sample and are also refracted upon entering or leaving the sample. The light-polarization directions are therefore poorly defined. Immersing the sample in a liquid that has a refractive index close to that of the polymer helps to minimize this problem [4],... 

Polarization effects are another feature of Raman spectroscopy that improves the assignment of bands and enables the determination of molecular orientation. Analysis of the polarized and non-polarized bands of isotropic phases enables determination of the symmetry of the respective vibrations. For aligned molecules in crystals or at surfaces it is possible to measure the dependence of up to six independent Raman spectra on the polarization and direction of propagation of incident and scattered light relative to the molecular or crystal axes. 

In the Bom-Oppenheimer picture the nuclei move on a potential energy surface (PES) which is a solution to the electronic Schrodinger equation. The PES is independent of the nuclear masses (i.e. it is the same for isotopic molecules), this is not the case when working in the adiabatic approximation since the diagonal correction (and mass polarization) depends on the nuclear masses. Solution of (3.16) for the nuclear wave function leads to energy levels for molecular vibrations (Section 13.1) and rotations, which in turn are the fundamentals for many forms of spectroscopy, such as IR, Raman, microwave etc. 

Recently, the In situ Raman scattering from Fe-TsPc adsorbed onto the low Index crystallographic faces of Ag was examined and the results obtained are shown In Fig. 5 (15). On the basis of the similarities of these spectra with those obtained for the macrocycle In solution phase, as well as the polarization behavior characteristics, It has been concluded that the most likely configuration Is that with the macrocycle edge-on with respect to the surface. This Is In agreement with conclusions reached from the UV-vlslble reflectance spectra. The preferred configuration, however, may depend on the particular macrocycle, as well as on the nature of the adsorption site. 

K. Kneipp, A. Jorio, H. Kneipp, S.D.M. Brown, K. Shafer, J. Motz, R. Saito, G. Dresselhaus, and M.S. Dresslhaus, Polarization effects in surface-enhanced resonant Raman scattering of single-wall carbon nanotubes on colloidal silver clusters. Phys. Rev. B 63, 081401.1-081401.4 (2001). 

Nonresonance Raman spectra of the alternating LB films were measured by a total reflection method shown in Figure 23. The films were deposited on quartz prisms. The s-polarized beam of 647.1 nm from a Kr laser was incident upon the interface between the quartz and film at an angle of 45° from the quarz side, and totally reflected. Raman line scattered from the film in the direction of 45° from the surface was measured through a Spex Triplemate by a Photometries PM512 CCD detector with 512x512 pixels operated at -125 °C. The spectral resolution was about 5 cm 1. 

The combination of surface enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) provides an effective in-situ approach for studying the electrode-electrolyte interface. The extreme sensitivity to surface species of SERS is well known. By using polarization modulation of the infrared beam for IRRAS, the complete band shape is obtained without modulating the electrode potential. 

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

---