The theory of Surface Enhanced Hyper Raman Scattering (A review)

The Dipole Quadrupole theory of Surface Enhanced Hyper Raman Scattering (SEHRS), created by the authors is expounded in detail. Peculiarities of behavior of electromagnetic field on rough metal surfaces are considered. It is demonstrated that there is an enhancement of the dipole and quadrupole light-molecule interaction near the places of the surface with a large curvature. The expression for the SEHRS crosssection of symmetrical molecules is obtained. Selection rules for the scattering contributions are derived and a qualitative classification of the contributions after the enhancement degree is performed. Analysis of experimental spectra of pyrazine and phenazine, and also some another molecules is performed too. It is demonstrated a full coincidence of experimental regularities in these spectra with the theory suggested.     

Group-Theoretical Interpretation of Surface-Enhanced Raman Scattering Spectra of Copper Phthalocyanine Adsorbed on Gallium Phosphide

Optics and Spectroscopy - Spectra of surface-enhanced Raman scattering of a copper phthalocyanine molecule adsorbed on a GaP substrate are studied. It is shown that very strong lines forbidden in...     

Peculiarities of the SEHRS spectrum of 4,4′-bipyridine molecule

The SEHRS spectrum of 4,4′-bipyridine is analyzed on the base of the Dipole-Quadrupole theory. It is demonstrated that there appear strong lines caused by vibrations transforming after the unit irreducible representation of the D₂ symmetry group, which is most probably describes the symmetry properties of the molecule. These lines are nearly forbidden for the molecule, adsorbed on rough metal surfaces. Appearance of these lines is associated with a strong quadrupole light–molecule interaction, which exists in this system. In addition, there are lines caused by contributions from both the vibrations transforming after the unit irreducible representation A and the representation B₁, which describes transformational properties of the d_z component of the dipole moment, which is perpendicular to the surface. This result is associated with the specific geometry of the molecule, when the indicated vibrations can be nearly degenerate and cannot be resolved by the SEHRS spectra analysis. Analysis of the SEHRS spectra for the possible geometry of the molecule with the D_2h symmetry group leads to similar results. This issue is in a full coincidence with the results of the SEHRS Dipole-Quadrupole theory.     

Raman Spectra of Glycine and Their Modeling in Terms of the Discrete–Continuum Model of Their Water Solvation Shell

Optics and Spectroscopy - Raman spectra of glycine in a crystalline form and in a water environment have been obtained. B3LYP/6-311++G(3df,2p) quantum-chemical calculations have shown that an...     

The theory of SERS on semiconductor and dielectric substrates

It is demonstrated that the reason for SERS on dielectric and semiconductor substrates is enhancement of the electric field in the regions of the tops of surface roughness with a very small radius or a very large curvature. The enhancement depends on the dielectric constant of the substrate and is stronger for a larger dielectric constant. It is indicated that the enhancement on dielectrics and semiconductors is weaker than on metals with the same modulus of the dielectric constant. The result obtained is confirmed by experimental data on the enhancement coefficients obtained for various semiconductor and dielectric substrates.     

The results from ten years of measuring several parameters of the antarctic atmosphere with tethered balloons

The results from measuring several parameters of the Antarctic atmosphere’s lower layers over the period 2004 through 2014 (Russian Antarctic expeditions 49 through 59) are presented. Such atmospheric parameters as the altitude dependence of the velocity and direction of the ground wind, the level of background radiation, and the concentrations of ozone and singlet oxygen are studied. Devices are installed on board the vessel Akademik Fedorov and at Antarctic ground stations. Tethered balloons are also used.     

Electrodynamical forbiddance of a strong quadrupole interaction in surface enhanced optical processes. Experimental confirmation of the existence in fullerene С<Subscript>60</Subscript>

It is demonstrated that in the SERS and SEIRA spectra of the fullerene С₆₀, the lines, which are forbidden in usual Raman and IR spectra and allowed in SERS and SEIRA, are absent. In addition the enhancement SERS coefficient in a single molecule detection regime is ~10⁸ instead of the value 10¹⁴–10¹⁵, characteristic for this phenomenon. These results are explained by the existence of so-called electrodynamical forbiddance of a strong quadrupole light-molecule interaction, which arises because of belonging of C⁶⁰ to the icosahedral symmetry group and due to the electrodynamical law divE = 0.     

Withdrawal of Electrodynamical Forbiddance and Peculiarities of the SERS Spectra in Fullerene C<Subscript>70</Subscript>

It is demonstrated that in fullerene C₇₀, which can be considered as a deformed fullerene C₆₀ in some mean sense there is a withdrawal of an Electrodynamical forbiddance of a strong quadrupole light-molecule interaction, which is realized in the fullerene C₆₀. This situation occurs because of the reduction of symmetry of C₆₀ from the icosahedral symmetry group Y_h to the group D_5h. The withdrawal results in appearance of the lines in the SERS spectra of C₆₀, which are forbidden in usual Raman scattering and are active in the infrared absorption spectra. The experimentally measured SERS spectra of C₇₀ demonstrates existence of such lines that strongly confirms our ideas about the dipole-quadrupole SERS mechanism.     

Hydroxyapatite/Anatase Photocatalytic Core–Shell Composite Prepared by Sol‒Gel Processing

The conditions for preparing hydroxyapatite/anatase Ca₁₀(PO₄)₆(OH₎₂/TiO₂ nanocomposites with a core–shell structure by sol?gel processing have been optimized. The photocatalytic activity of these nanocomposites is close to that of the commercial photocatalysts based on titanium dioxide (precursor Ti(OBut)₄ concentration 40 vol %, hydroxyapatite/TiO₂ sol ratio 1: 2, annealing temperature 500°C). The photocatalytic activity of hydroxyapatite/TiO₂ composites with different anatase contents has been estimated for the first time from the singlet oxygen yield. It is shown that the degree of modification of apatite particle surface affects significantly the structural characteristics of the hydroxyapatite/TiO₂ composite. An increase in the relative anatase content reduces the sizes of apatite crystallites and increases their specific surface.