Showing papers on "Raman spectroscopy published in 1972"

Raman Oscillation in Glass Optical Waveguide

Abstract: Stimulated Raman emission in the visible has been observed in glass‐fiber optical waveguides. Even though the Raman cross section is quite small, relatively low threshold for Raman emission can be achieved because high optical power densities are maintained over long lengths of waveguide. The broad stimulated gain bandwidths available in glass should permit the construction of wide‐band fiber amplifiers and Raman oscillators tunable over a range of 100 A.

Raman Scattering: Orientational Motions in Liquids

Abstract: A systematic study of reorientational motions by Raman scattering is undertaken for 10 liquids. The theory of orientational broadening of Raman lines is presented with emphasis on the use of symmetry of molecular vibrations to obtain information of reorientational motions about different axes. The rotational diffusion tensor of benzene was obtained and found to be approximately isotropic. The time for reorientation of the major molecular axis was measured for nine liquids and the mechanism for reorientation for these liquids discussed. Liquids are classified according to whether reorientation is determined by structural dynamics or collisional motions. Finally it was possible to obtain the time between collisions for liquids in which reorientation is collision limited and occurs in small angular steps.

Analysis of Orientational Broadening of Raman Line Shapes

Abstract: A systematic investigation of orientational broadening of Raman vibrational lines is undertaken and measurements of line shapes are made for 19 liquids. The problem of separating orientational broadening from the intrinsic vibrational lineshape is discussed in detail and a method of analysis is presented. The advantages and limitations of this method are considered and compared to an earlier method proposed by Rakov [Tr. Fiz. Inst. Akad. Nauk SSSR 27, 111 (1964); Opt. Spectrosc. 7, 128 (1959)]. The intrinsic width is determined for each line studied and removed from the spectrum to give the orientational broadening. It is noted that the intrinsic line shape, measured from polarized Raman spectra, may be used to correct infrared vibrational spectra which suffer from the same problems. It is shown that neglect of intrinsic width can lead to significant errors in the interpretation of the infrared data.

Resonance Raman Spectra of Hemoglobin and Cytochrome c: Inverse Polarization and Vibronic Scattering

Abstract: Resonance Raman spectra of hemoglobin and cytochrome c in dilute solution contain prominent bands that exhibit inverse polarization, i.e., the polarization vector of the incident radiation is rotated through 90° for 90° scattering, giving infinite depolarization ratios. This phenomenon is shown to require an antisymmetric molecular-scattering tensor. The antisymmetry, which is characteristic of resonance scattering, is associated with the form of a particular class of vibrations, A20, of the tetragonal heme chromophores. The dependence of the resonance Raman spectra on the wavelength of the exciting radiation, as well as their polarization properties, demonstrates that the prominent bands correspond to vibronically active modes of the first electronic transition of the heme proteins, and provide confirmation of Albrecht's vibronic theory of Raman intensities.

Raman scattering and theoretical studies of Jahn—Teller induced phase transitions in some rare-earth compounds

Abstract: The rare-earth crystals DyVO 4 , DyAsO 4 and TbVO 4 undergo structural phase transitions at 14, 12 and 34 K respectively induced by a cooperative Jahn-Teller effect. An experimental investigation of the phase changes has been made using Raman scattering methods. For purposes of comparison, the Raman spectra of DyPO 4 , YVO 4 and GdVO 4 (which do not undergo phase transitions) have also been measured. A detailed theory of the phase transitions has been developed which accounts for the electronic and vibrational Raman spectra. The lowest four electronic levels of Dy 3+ and Tb 3+ are treated in a pseudospin formalism, and the theory is discussed in terms of mixed phonon and pseudo-spin excitations. The singly degenerate κ ≈ 0 optic phonons are not measurably affected by the transitions, but splittings of up to 20 cm -1 developed in the doubly degenerate E g phonon modes in the Raman spectra owing to anharmonic couplings with the electronic states. Splittings are also observed in the lowest electronic levels of the rate earth ions below the transition temperature; these electronic modes effectively constitute the soft mode which causes the transitions to occur. A molecular field model is first used in the theoretical analysis. The equations of motion of the coupled excitations are then found and the energies, line widths and dispersion of the mixed excitations are discussed. The connexion between the static strain and the acoustic phonon mode coupling is investigated, and a thermodynamic treatment of the elastic constants is given. From the Raman data, it appears that in TbVO 4 the acoustic mode coupling is stronger than the optic mode coupling.

Reorientation and Vibrational Relaxation as Line Broadening Factors in Vibrational Spectroscopy

Abstract: The theory of Gordon which relates the shape of the depolarized components of certain Raman bands to a molecular reorientation correlation function is extended to a number of types of molecular vibrations not previously covered. In addition, the contribution to the line shape for vibrational relaxation and reorientation is obtained for the three types of vibrational spectroscopy, infrared, Raman, and hyper‐Raman, and it is shown that the form of the vibrational relaxation contribution is the same for each spectroscopy. Conditions and assumptions are given under which the line broadening contributions of reorientation and vibrational relaxation can be separated and experimentally determined.

Biological Sciences: One and Two-dimensional Structure of Alpha-Helix and Beta-Sheet Forms of Poly( L -Alanine) shown by Specific Heat Measurements at Low Temperatures (1.5–20 K)

Abstract: HOMOPOLYPEPTIDES provide good model systems for various aspects of proteins1,2. Recent advances in high polymer and solid state physics have enabled the vibrational aspects of the simpler homopolypeptides to be treated as normal—but complicated—polymers by the theoretical techniques of lattice dynamics based on the experimental methods of neutron, infrared and Raman spectroscopy. Basically, however, these latter methods examine the optical vibrational modes of a system, that is, those modes which are of energy higher than, for example, 70 cm−1. The important lower-energy modes are well examined by specific heat measurements, which do not require single crystal samples, at low temperatures (for example, 1–20 K, where only the acoustic modes are excited thermally to any appreciable extent—1 K∼0.7 cm−1). The low temperature measurements presented here are the first made on a polypeptide in alpha and beta-conformation, and clearly show the one-dimensional nature of the α-helix and the two-dimensional nature of the β-sheet structure. Quantitatively, these measurements also provide tests of theories of published vibrational models of homopolypeptides, and will give hydrogen bond strengths.

Determination of the backbone structure of nucleic acids and nucleic acid oligomers by laser Raman scattering.

Abstract: Raman spectra of fibers of DNA that have been prepared in the A, B, and C forms are presented and compared with Raman spectra of DNA and RNA in dilute solution. It is shown that the phosphate vibrations in the region 750-850 cm-1 are very sensitive to the specific conformation of the phosphate group in the backbone chain and are virtually independent of all ohter factors. Thus, a very simple method for the determination of the specific conformation of the backbone chain of nucleic acids, at least so far as the sugar-phosphate chain is concerned, appears available. The method is applied to short oligomers and dimers of ribonucleosides. It is found that at low temperatures, at pH 7, the phosphate group goes into the geometry of the A conformation when the stacking forces between the bases are sufficiently strong.

Vibrational spectra and structure : a series of advances

Abstract: 1. Applications of Matrix Infrared Spectroscopy to Mapping of Bimolecular Reaction Paths (H. Frei). Introduction. Oxygen Transfer Reactions. Hydrogen Transfer Reactions. Concluding Remarks. 2. Vibrational Line Profile and Frequency Shift Studies by Raman Spectroscopy (B.P. Asthana, W. Kiefer). Introduction. Deconvolution of Raman Line Profile. Determination of Frequency Shifts by Raman Difference Spectroscopy (RDS). Study of Linewidth Changes by RDS. Experimental Techniques. Applications. Summary. 3. Microwave Fourier Transform Spectroscopy (A. Bauder). Introduction. Experimental. Rotational Spectra. 4. Ab Initio Quality of SCMEH-MO Calculations of Complex Inorganic Systems (E.A. Boudreaux). Introduction. Theoretical Foundation. Applications and Results. Comments, Conclusions and Acknowledgments. 5. Calculated and Experimental Vibrational Spectra and Force Fields of Isolated Pyrimidine Bases (W.B. Person, K. Szczepaniak). Introduction. Methods for Study of Isolated Molecules. Stabilities, Structures, and Dipole Moments of Isolated Pyrimidine Bases. Comparison of Experimental and Calculated Infrared Spectra for Pyrimidine Bases. Basis Set Dependence of Calculated Infrared Spectra and Vibrational Parameters for Uracil. Comparison of Spectra Calculated for Uracil, Thymine, Cytosine, and 1-Methylcytosine. Comparison and Transferability of Bond Force Constants from Thymine, Uracil, Cytosine, and 1-Methylcytosine. Comparison and Transferability of Bond Dipole Derivatives from Uracil, Thymine, Cytosine, and 1-Methylcytosine. Concluding Remarks. Author Index. Subject Index.

Measurement of Atmospheric Temperature Profiles by Raman Backscatter

Abstract: A technique for measuring instantaneous atmospheric temperature profiles is given. Utilizing the portion of the laser backscatter arising from the Raman rotational spectrum of N2, profiles up to 2 km with 100 m depth resolution provide temperature to within a degree with signal-to-noise ratios of order unity. Examples are given.

Conformationally dependent low-frequency motions of proteins by laser Raman spectroscopy.

Abstract: Low-frequency Raman bands (lower than 50 cm(-1)) exist in certain proteins. They are dependent upon the conformation of the protein molecule, but are relatively independent of the form of the sample, i.e., whether it is a film or a crystal.Low-frequency Raman spectra were obtained from samples of alpha-chymotrypsin that had been prepared in several ways. A peak at about 29 cm(-1) was found for all samples except the one that had been denatured with sodium dodecyl sulfate. Such low frequency motions must arise from vibrations that involve all, or very large portions, of the protein molecule.

A vibrational-spectroscopic study of the species present in the CO2−H2O system

Abstract: Raman and infrared spectra have been recorded of water and heavy-water solutions of carbon dioxide, potassium bicarbonate, and potassium carbonate. The structures of the carbonate and bicarbonate ions and CO2 (aqueous solution) have been determined from a consideration of Raman and infrared data. The results reveal the presence of solvent effects in the carbonate and CO2 water solutions. No bands characteristic of H2CO3 were observed in the Raman spectrum of aqueous solutions of CO2.

Remote measurements of the atmosphere using Raman scattering.

Abstract: Raman optical radar measurements of the atmosphere demonstrate that the technique may be used to obtain quantitative measurements of the spatial distribution of individual atmospheric molecular trace constituents (in particular water vapor) and of the major constituents. It is shown that monitoring Raman signals from atmospheric nitrogen aids in interpreting elastic scattering measurements by eliminating attenuation effects. In general, the experimental results show good agreement with independent meteorological measurements. Finally, experimental data are utilized to estimate the Raman backscatter cross section for water vapor excited at 3471.5 A.

Raman and Infrared Spectral Investigations of Water Structure

Abstract: The models that have been proposed to represent the structure of liquid water are too numerous to be described here, but they are discussed in Chapter 14. Two general classes of models of interest for present purposes are usually designated by the terms continuum(1132) and mixture.(356) Continuum models treat water in terms of a continuous distribution of interactions that are presumed to be spectroscopically indistinguishable, whereas mixture models generally relate distinct spectral features to structures differing in the extent of hydrogen bonding. Some of the earlier spectroscopic investigations(1132) appeared to favor continuum models, but recent laser- Raman investigations(1138) as well as results from nonlinear optical techniques such as stimulated Raman scattering and hyper-Raman or inelastic harmonic light scattering strongly favor mixture models, e.g., the consecutive hydrogen-bond disruption model.

Vibrational spectroscopy of solids

Abstract: This 1972 monograph is devoted to the analysis and interpretation of the infrared and Raman spectra of solid compounds, frequently used for their identification and characterization. It was thought unsatisfactory to analyse such spectra by the theory applicable to gas-phase samples, though this was frequently done. Furthermore, the results obtained by far infrared and laser Raman spectrometers, which detect the movement of atoms and/or molecules as a whole, had no gas-phase analogy. A separate approach to solid state vibrational spectra was therefore proposed within this volume. Dr Sherwood describes the solid state physics of vibrational spectroscopy and extends it to the more complex structures of low symmetry. He assumes an understanding of the infrared and Raman spectra of gases.

Raman Spectra of α and β Cristobalite

Abstract: Raman spectra of polycrystalline crystobalite were measured over the frequency interval of the fundamental optical modes from 77°K to 538°C. Spectra recorded above and below the α–β transition temperature were strikingly different. The strong bands measured at 416 and 230 cm−1 with α cristobalite at 25°C were not observed from spectra of the β phase. The Raman spectrum of β cristobalite exhibited only three bands and, in contrast to crystalline quartz, a strongly temperature dependent band was not observed from measurements at temperatures near the transition point. Infrared reflection spectra of α cristobalite also were recorded, and the longitudinal optical mode frequencies were determined. Raman spectra of β cristobalite showed that the structure of this material should not be employed as a lattice model for noncrystalline SiO2.