Showing papers on "Raman spectroscopy published in 1971"

Infrared and Raman Spectra of Zirconia Polymorphs

Abstract: The infrared and Raman frequencies of monoclinic zirconia and of stabilized and metastable tetragonal and cubic zirconias were established. Infrared spectra were examined by the powder transmission (CsI pellet) and surface reflection techniques. The effects of heating, grinding, and adding stabilizing oxides on the ir spectra were determined. The spectra develop additional bands as the crystal symmetry is lowered, and certain of these bands are highly sensitive to strain-induced distortions of the crystal lattice. Practical applications of ir and Raman spectroscopy to zirconia technology are discussed.

Rayleigh and Raman scattering from optically active molecules

Abstract: The intensity of Rayleigh and Raman scattering from optically active molecules is shown to be slightly different in right and left circularly polarized incident light. The circular intensity differential of the Rayleigh line is dependent on components of the optical activity tensor, and that of the Raman lines is a function of the variation of the optical activity with the vibrational coordinates. This circular intensity differential might be of the order of 10-3 times that of the Rayleigh or Raman intensity.

On the Dependence of Vibrational Raman Intensity on the Wavelength of Incident Light

Abstract: Experiments on the wavelength dependence across the visible region of the intensity of the 1334‐cm−1 Raman line of p‐nitroaniline (PNA) are analyzed from a general theoretical viewpoint. When theory is simplified to correspond to the PNA example, two obvious sources of Raman intensity are apparent. One is based on a possible shift of equilibrium nuclear position along the 1334‐cm−1 mode upon exciting PNA into its first excited singlet state (in the near ultraviolet). The other source deals with vibronic coupling of the first excited electronic state with a whole family of states in the deep ultraviolet having similar polarizations. It is seen how this second mechanism appears to be the dominant one in this case. The absolute scattering cross section for the 1334 cm−1 is given and is found to agree with the order of magnitude estimates calculated theoretically.

Raman Spectra and Lattice Dynamics of Tellurium

Abstract: The Raman spectrum of trigonal tellurium has been obtained at 295 and 90 \ifmmode^\circ\else\textdegree\fi{}K. The Raman-active ${A}_{1}$ singlet and two $E$ doublets are identified by the scattering polarization selection rules, and the $E$-mode LO-TO splittings and linear wave-vector shifts are observed. The natural linewidths of the phonons are resolved and some weak second-order structure is evident. A spectrum of amorphous tellurium is also presented. The data on trigonal tellurium, together with neutron-scattering and infrared reflectivity measurements, are used to construct a lattice-dynamical model based on a symmetrized Fourier-expansion scheme incorporating generalized noncentral forces.

Raman Spectra of Amorphous Si and Related Tetrahedrally Bonded Semiconductors

Abstract: Raman scattering has been studied in the amorphous form of Si and several related, tetrahedrally bonded semiconductors (Ge, GaAs, GaP, InSb). All vibrational modes of the material can take part in the scattering process, and the Raman spectrum is a measure of the density of vibrational states. The amorphous phases are found to have vibrational spectra very similar to the corresponding crystals, reflecting the similarity in short-range order of the two phases.

Laser Raman investigation of the effect of cholesterol on conformational changes in dipalmitoyl lecithin multilayers.

Abstract: Large and abrupt changes are observed at 38°C in the 1100 cm-1 region of the Raman spectrum of aqueous dipalmitoyl lecithin multilayers. They correspond to conformational changes due to the melting of the paraffin side chains. The addition of cholesterol to the multilayers broadens but does not abolish these changes. It is suggested that the addition of cholesterol decreases the interactions between adjacent paraffin side chains of lecithin, causing a change from a cooperative to a noncooperative gel-liquid crystal transition. Removal of water from dipalmitoyl lecithin also results in a noncooperative transition strikingly similar to that caused by addition of cholesterol. Raman spectroscopy thus provides a new and sensitive probe for analyzing the structures of membranes and their constituents.

Infrared Absorption and Raman Scattering by Two-Magnon Processes in NiO

Abstract: Strong two-magnon ($2M$) Raman scattering has been observed from NiO along with first- and second-order phonon scattering The shape of the $2M$ scattering peak is well described by a simple-cubic Green's function for interacting spin waves with an intersublattice exchange ${J}_{2}$ = 148 ${\mathrm{cm}}^{\ensuremath{-}1}$ The temperature shift of the scattering peak is identical to that of the 2000-${\mathrm{cm}}^{\ensuremath{-}1}$ ir absorption peak described by Newman and Chrenko, but energy considerations require the absorption peak to be a phonon sideband of the $2M$ scattering peak, which is not seen in absorption

Dynamics of the rutile structure. III. Lattice dynamics, infrared and Raman spectra of SnO2

Abstract: For Pt. II see abstr. A71824 of 1970. The polarized infrared reflection absorption and laser Raman spectra have been recorded at both 300K and 100K for single crystals of SnO2. The dielectric parameters epsilon ' and epsilon " have been derived and the optically active transverse and longitudinal k=0 phonon frequencies found. The elastic constants and the dispersion curves for phonons propagating along (0,0, xi ) and ( xi , xi ,0) are calculated using a rigid ion model with short range central axially symmetric forces and long range Coulomb forces which gives satisfactory agreement with the experimentally observed frequencies. The principal force constants and the effective charges on the ions are compared with those for other crystals with the rutile structure. The multiphonon infrared absorption is compared with theoretical predictions based on selection rules and the calculated phonon dispersion curves. The hydroxyl ion impurities are shown to be oriented parallel to the crystal's optic axis.

The vibrational spectrum of zircon (zrsio4)

Abstract: This paper reports polarized infrared and raman studies on zircon, zrsio4. The 36 k=0 modes of vibration are classified using group theoretical methods. The dielectric parameters epsilon minutes and epsilonseconds have been derived from the reflection spectrum using kramers-kronig theory. Measurements have also been made on the elements of the raman polarizability tensor, and the angular dependence of the scattered intensity has been studied for several bands. The crystal field splittings of the vibrational levels of the silicate ions are large, but some simple force constant considerations lead to the conclusion that the silicate ions are essentially molecular units.

Raman Study of Liquids. I. Theory of the Raman Spectra of Diatomic Molecules in Inert Solutions

Abstract: A theory is proposed to explain the Raman spectra of inert solutions of diatomic molecules; this theory can also be considered as an approximate theory of Raman spectra of pure liquids The theory is a stochastic-type theory related to similar theories of infrared and NMR spectra The vapor-solution band shifts are shown to depend on the difference between the solvent-solute interaction energies of the two vibrational states involved in the transition The analysis of the band profiles is made separately for the isotropic and anisotropic components, respectively, of a Raman spectrum The former spectrum is produced by vibrational relaxation mechanisms alone; the bands are all asymmetric although, in certain cases, the asymmetric perturbation is small enough to be neglected The latter spectrum is produced by both vibrational and reorientational relaxation mechanisms The theory predicts the existence of a continuous sequence of band forms comprising, among others, the profile with an $O\ensuremath{-}Q\ensuremath{-}S\ensuremath{-}$ type structure, the Lorentzian profile, the Gaussian profile, the Voigt profile, and several sorts of asymmetric profiles The resulting Raman spectrum appears as a superposition, with appropriate coefficients, of an isotropic and anisotropic spectrum A procedure is indicated permitting a separate study of vibrational and reorientational relaxation effects

Conformational dependence of the Raman scattering intensities from polynucleotides. III. Order-disorder changes in helical structures

Abstract: Raman spectra are presented on ordered and presumably helical structures of DNA and RNA as well as the poly A·poly U helical complex, polydAT, and the helical aggregates of 5′-GMP and 3′-GMP The changes in the frequency and the intensity of the Raman bands as these structures undergo order-disorder transitions have been measured In general the changes we have found can be placed into three categories: (1) A reduction in the intensities of certain ring vibrations of the polynucleotide bases is observed when stacking or ordering occurs (Raman hypochromism) Since the ring vibrational frequencies are different for each type of base, we have been able to obtain some estimate of average amount of order of each type of base in partially ordered helical systems (2) A very large increase in the intensity of a sharp, strongly polarized band at about 815 cm−1 is observed when polyriboA and polyriboU are formed into a helical complex Although this band is not present in the separated chains at high temperature, a broad diffuse band at about 800 cm−1 is present The 815 cm−1 band undoubtedly arises from the vibrations of the phosphate-sugar portions of the molecule and provides a sensitive handle to the back-bone conformation of the polymer This band also appears upon ordering of RNA, formation of the helical aggregate of 5′-riboGMP, and to some extent in the selfstacking of the polyribonucleotides polyA, polyU in the presence of Mg++, PolyC, and polyG No such intense, polarized band is found, however, in ordered DNA, polydAT, or the 3′-riboGMP aggregate, although there is a conformationally independent band at about 795 cm−1 in DNA and polydAT (3) Numerous frequency changes occur during Conformational changes In particular the 1600–1700 cm−1 region in D2O shows significant conformationally dependent changes in the CO stretching region analogous to the changes in this region which have been observed in these substances in the infrared Thus, Raman scattering appears to provide a technique for simultaneously observing the effects of base stacking, backbone conformation and carbonyl hydrogen bonding in nucleic acids in moderately dilute (10–25 mg/ml) aqueous solutions

Conformational dependence of the Raman scattering intensities from polynucleotides.

Abstract: The intensity of Raman scattering from the various Raman active vibrations of poly-(riboadenylic acid), poly(ribocytidylic acid), poly(ribouridylic acid), and poly(riboinosinic acid) in moderately dilute solutions were examined as the temperature was changed to alter their conformation. It was found that certain highly intense, highly polarized Raman bands from the totally symmetric, i.e., in-plane, ring vibrations of the nucleic acid bases become less intense as the chains become more ordered in solution. Since these vibrations occur at frequencies which are markedly different for each type of base, Raman spectroscopy appears to provide a new method for the characterizing of the average conformation of each of the bases in solution. A theory for the resonant Raman effect is given in which it is shown that, a decrease in resonant Raman intensity is to be expected if one obtains a decrease in the intensity of the corresponding ultraviolet absorption band with which the incident light is resonant. If it is assumed that certain Raman bands derive their intensity predominantly from the first few ultraviolet absorption intensities, then a qualitative explanation of our observed conformational dependence of the ordinary Raman intensities can be obtained.

Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals

Abstract: The singlet–triplet (T1 ← S0) excitation spectrum for delayed fluorescence and the prompt fluorescence (S1 → S0) emission spectrum have been measured for a tetracene crystal at room temperature. The origin (0–0 transition) in the two spectra at 10 100 ± 20 and 18 680 ± 30 cm−1, respectively, imply the activation energy for singlet exciton fission, ΔE = 1520 ± 70 cm−1. Raman lines corresponding to the vibrational structure in the above spectra were detected. The fluorescence emission spectra show the need for taking reabsorption effects into account.

A Cell for Resonance Raman Excitation with Lasers in Liquids

Abstract: The experimental observation of the resonance Raman effect in solutions with laser excitation is restricted by the absorption of the sample. Due to the thermal lens effect it is not possible to get a sharp laser focus in highly absorbing media. Under ordinary circumstances one is required to compromise between absorption and emission of the scattered light—that means discovering optimal solution concentrations and suitable laser power or focusing conditions to get the smallest degradation of the laser beam.

Raman and Infrared Spectral Studies of Anhydrous Li2CO3 and Na2CO3

Abstract: The infrared and Raman spectra of anhydrous crystalline Li2CO3 and Na2CO3 were measured at 300 and at 80°K. Bands observed in the vibrational spectra of Li2CO3 were assigned according to the C2h factor group symmetry. The doublet structure observed for each of the internal modes in the spectra of Na2CO3 was interpreted in terms of an ordered arrangement of CO3= ions over two nonequivalent orientations within the primitive cell. Multiple internal reflection and polarized specular reflectance techniques were used to determine transverse optical (TO) and longitudinal optical (LO) mode frequencies in Li2CO3 and Na2CO3. It was shown from these measurements that the infrared transmission spectra of these compounds exhibit band maxima which are admixtures of LO and TO modes.

Raman and Infrared Spectral Studies of Anhydrous Li2CO3 and Na2CO3

Abstract: The infrared and Raman spectra of anhydrous crystalline Li2CO3 and Na2CO3 were measured at 300 and at 80°K. Bands observed in the vibrational spectra of Li2CO3 were assigned according to the C2h factor group symmetry. The doublet structure observed for each of the internal modes in the spectra of Na2CO3 was interpreted in terms of an ordered arrangement of CO3= ions over two nonequivalent orientations within the primitive cell. Multiple internal reflection and polarized specular reflectance techniques were used to determine transverse optical (TO) and longitudinal optical (LO) mode frequencies in Li2CO3 and Na2CO3. It was shown from these measurements that the infrared transmission spectra of these compounds exhibit band maxima which are admixtures of LO and TO modes.

Theory of the One-Phonon Resonance Raman Effect

Abstract: Resonant enhancements of Raman scattering cross sections for photons near electronic resonances are calculated for ordinary allowed scattering and for intraband Fr\"ohlich scattering, which is of higher order in the wave vectors and thus forbidden. Exciton effects are included exactly in the hydrogenic approximation via numerical calculations using the Green's-function formulation. Much greater enhancements are found for forbidden than for allowed lines, and it is shown that forbidden lines can become comparable to allowed lines near resonance with large Wannier excitons. It is predicted to be feasible to observe one-LO-phonon lines in crystals (e.g., TlCl and TlBr) in which such transitions are always forbidden. Comparison with experiment for CdS is presented.

Raman Spectrum of Semiconducting and Metallic V O 2

Abstract: The Raman scattering spectrum of V${\mathrm{O}}_{2}$ is reported between 4.2 and 600\ifmmode^\circ\else\textdegree\fi{}K. In the semiconducting monoclinic phase only sharp phonon structure is observed. The metallic rutile phase exhibits a pronounced softening and damping in the observed phonon spectrum. This evidence supports a recently proposed phenomenological mechanism for the semiconductor-to-metal transition.

Breakdown of Selection Rules in Resonance Raman Scattering

Abstract: Large 1LO Raman scattering near resonance in CdS is observed in the diagonal components of the Raman tensor ${R}^{\ensuremath{\alpha}\ensuremath{\alpha}}$ independent of crystal-symmetry selection rules. The data support the interpretation as an intrinsic bulk effect dependent on the finite wavelength of light.

Rotating Raman Sample Technique for Colored Crystal Powders; Resonance Raman Effect in Solid KMnO4

Abstract: A simple sample technique which makes it possible to record Raman spectra of highly absorbing solids is described. The main feature is a rotating sample system containing pressed crystal powders, on which the laser beam is focused. The relative motion between laser focus and sample surface avoids heating and decomposition of the crystal powder. With this technique it is, for instance, possible to obtain a Raman spectrum of solid potassium permanganate, displaying a progression of strongly resonance enhanced overtones of the totally symmetric permanganate mode as well as a well-defined weakly enhanced spectrum for the other internal modes.

Optical Phonon Lifetime Measured Directly with Picosecond Pulses

Abstract: The lifetime of the 1086-${\mathrm{cm}}^{\ensuremath{-}1}$ optical phonon in calcite is measured directly to be 8.5 \ifmmode\pm\else\textpm\fi{} 2 psec at 297\ifmmode^\circ\else\textdegree\fi{}K and 19.1 \ifmmode\pm\else\textpm\fi{} 4 psec at 100\ifmmode^\circ\else\textdegree\fi{}K by using a picosecond laser beam to create the phonons by stimulated Raman scattering, and then observing Raman scattering off the phonons at various delay times with a weaker picosecond beam at another frequency.

Vibrational Raman Spectra of CaMoO4 and CaWO4 at High Pressures

Abstract: Raman vibrational spectra at pressures as high as 40 kbar are reported for the scheelite and previously unknown high‐pressure phases of CaMoO4 and CaWO4. The pressure derivatives of the vibrational frequencies, dν / dP, are all between 0.0 and 1.0 cm−1·kbar−1 which is normal for ionic crystals; however, the observed pressure dependences of the frequencies of the internal modes are qualitatively different from those predicted according to Scott's interpretation of the splittings of the scheelite spectra. The appearance of the high‐pressure phases is indicated by splittings of Eg modes at 145 and 797 cm−1 in CaMoO4 and 117 and 797 cm−1 in CaWO4. The spectra of the high‐pressure phases and the dependences of the apparent transition pressures upon orientation of the crystallographic axes relative to the small stress anisotropy in the high‐pressure cell suggest that the high‐pressure phases have structures similar to that of NiWO4.