Infrared spectra of thin films of α-crystalline hexafluoroethane: a manifestation of resonant dipole–dipole interaction in the range of fundamental vibrational modes ν<Subscript>5</Subscript> and ν<Subscript>10</Subscript>

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν₅ and ν₁₀ have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric ¹³С¹²СF₆ isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric ¹³С¹²СF₆ isotopologue with molecules of the environment, consisting of the most abundant ¹²C₂F₆ isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.     

Scattering of Polarized and Natural Light by a Monolayer of Spherical Homogeneous Spatially Ordered Particles under Normal Illumination

We consider distortions of the shapes of absorption bands of strongly scattering samples in the spectra of molecules adsorbed on the surface of dispersed solids. We show that the influence of the scattering on IR spectra of dispersed samples is not reduced merely to a weakening of the intensity of the transmitted light, but, rather, the scattering affects the contour of a spectral band due to changes in the refractive index of the substance in the range of the absorption band. Using carbon dioxide adsorbed on a NaX zeolite as an example, we demonstrate two methods for taking into account the contribution of the scattering to the spectra of surface compounds: the registration of the “diffuse-transmission” spectrum and placing a sample into an immersion liquid, for which liquid oxygen is used. The obtained spectra indicate that, if the zeolite is saturated with the adsorbate, the band of the antisymmetric stretching vibration of CO₂ molecules broadens and reveals a complex structure as a result of the resonant dipole–dipole interaction between adsorbed molecules.     

Growth and optical properties of BiI3 and PbI2 microcrystals

A study has been made of low-temperature absorption and luminescence spectra of bismuth iodate microcrystals in various hosts (layered cadmium iodate, microporous glasses and polymers), as well as of the spectra of mesoscopic domains formed in bulk bismuth iodate by mechanical strains. The structure of the spectra and the quantum shifts of the exciton levels yielded information on the dimensions and size dispersion of the microcrystals and domains, as well as on the effect of microcrystal size on the Stokes losses. The quantum exciton-line shifts in microcrystalline lead-iodate films grown in pores of the glass host have been used to calculate the film thicknesses. A photoinduced change in the mechanism of radiative recombination was observed in PbI₂ microcrystals. The spectrum of resonant Raman scattering in lead iodate microcrystals consists of broad bands corresponding to the branches of optical phonons undergoing strong angular dispersion. Fiz. Tverd. Tela (St. Petersburg) 40, 1724–1730 (September 1998)     

Absorption spectra of NaCl: Pb2+ at the A-band region

The origin of the absorption spectrum of NaCl:Pb²⁺ at the A-band region has been investigated. Main peaks are observed at 265, 273 and 290mμ in an untreated sample. In addition to the effect of lead concentration and thermal treatments, the luminescence and excitation spectra associated to the various bands have been determined. It is concluded that the 290 mμ band should be a composition of a number of bands corresponding to different types of simple dipole aggregates. The 265 mμ band, as well as the structure appearing in the region 220–260 mμ, is consistent with the existence of PbCl₂ precipitates.     

Very Low Frequency Far-Infrared Spectra of Mixtures of Dioxan with the Halogens and Related Molecules

Abstract

There has been considerable interest recently in the study of the submillimetre (or very far-infrared) absorption shown by both polar^1–4 and non-polar molecules.^2,5–8 Such absorption, in the ～5–100 cm^?1 region, for non-polar molecules is thought^2,6 to be caused by fluctuating dipoles associated with classical quadrupole-induced dipole interactions (in general multipole-induced dipole interactions). These effects are said to be “collision-induced” and can be thought of as being due to “collision” complexes in the liquid phase. For polar molecules the absorption is now thought^1–4 to be due to libration of the dipole in a “cage” of surrounding molecules (either molecules of the same species or of solvent). This so-called Poley-Hill model^9,10 is not inconsistent with the idea^1,2 of a residual rotation of the molecular dipole in the liquid phase. This similarity is underlined by the fact that some simple polar molecules^11,12 have a liquid phase Poley-Hill absorption the general shape and position of which follow quite closely that of the pressure broadened, gas phase spectrum. Our interest in the far-infrared region stems from our studies on halogen complexes with various n and bπ donors.^13,14 The pyridine-I₂ system (in cyclohexane) for example shows two bands in the far in frared not present in either component. The band at -183 cm is thought to be the stretching mode of the iodine, perturbed in the complex. The band at ～96 cm to the v(1-I) band, has so far been interpreted molecular″ stretching modebetween donor and acceptor, v(D-A).     

Polar properties of Langmuir-Blodgett films of copper phthalocyanines

Langmuir-Blodgett films of amphiphilic copper phthalocyanines are obtained. The Stark effect spectra and the spectra of pyro-and photosensitivity of these films are investigated. The following molecular parameters are determined: changes in the polarizability and the dipole moment for individual absorption bands in the Langmuir-Blodgett films and in an isotropic polymer solution. It is shown that the films obtained have photosensitivity due to the charge transfer in the spectral range 600–900 nm. The pyroelectric effect was observed, which indicates that the films have a polar structure.     

A theoretical study of the effect of disorder of the transition dipole moments of molecules on the shape of optical bands of molecular aggregates

Aggregates with substitutional disorder, in which molecules of different types have different transition dipole moments, are considered. The relations between the absorption spectra of aggregates with disordered and nondisordered transition dipole moments are obtained for two limiting cases: (1) the case when there is no statistical correlation between the transition energies and transition dipole moments of the molecules and (2) the case of total correlation, when the transition energies and transition dipole moments are strictly related to each other. For aggregates that are characterized by substitutional disorder along with diagonal disorder, an effective method of calculation of the optical bands is developed. Numerical calculations of the absorption bands of aggregates consisting of molecules of two types are carried out at different values of the parameters.     

Raman and IR spectra of K4Nb6O17and K4Nb6O17·3H2O single crystals

Polarised Raman and IR spectra of K₄Nb₆O₁₇ and K₄Nb₆O₁₇· 3H₂O single crystals were measured. The obtained spectra are discussed using the factor group approach for the orthorhombic P2₁nb space group and assignment of bands to the respective motions of atoms is proposed. In particular, we have shown that the bands above 770 cm⁻¹ can be attributed to the stretching modes of short niobium–oxygen bonds, which are present in this material due to the pronounced layered structure, whereas the potassium atoms contribute to the bands observed below 180 cm⁻¹. Our studies have revealed that intercalation of water molecules leads to shifts, broadening and changes in intensity of some bands. These changes have been attributed to slight changes in the bond lengths and angles, interactions of the water molecules with K atoms and structural disorder introduced by the intercalated water molecules. However, the main structural framework was preserved. Copyright © 2010 John Wiley & Sons, Ltd.     

Measurements of pressure-induced shifts in the 1-0 and 2-0 bands of HF and in the 2-0 bands of H35Cl and H37Cl

Fourier absorption spectra of HCl and HF measured at room temperature and low pressures were found to show evidence of pressure-induced shifts of the spectral lines at gas pressures of only 10 torr. Self-induced shifts were measured for the HF 2-0 band and for the H³⁵Cl and H³⁷ 2-0 bands. There were also measured in the same spectra shifts in the HF 2-0 band due to HCl and shifts in both HCl bands due to HF, with indications of shift oscillation due to near-resonant dipole-dipole interactions between HCl and HF. Separate measurements were made of pressure-induced shifts in the HF 1-0 and 2-0 bands and in both isotopic HCl bands, using separately argon, neon, nitrogen and carbon dioxide as the perturbing gases.     

Emission Spectra of BeO in Near Ultraviolet Region

Abstract

The emission spectra of isotopic BeO molecules as excited in low-pressure arc have been photographed in the region 300–350 nm at medium dispersion. The bands have been assigned to the c³II ? a³II system. The vibrational numbering was obtained from a study of the vibrational isotope effect. Vibrational constants for involved states are derived from least-squares fits of the measured bandhead wavenumbers.     

Evidence for Potassium-Sucrose Interaction in Biological Mid-Infrared Spectra by Multidimensional Analysis

Complex-formation between carbohydrates and cations could have important biological implications.

In this work, Mid-Infrared spectra of pure sucrose solutions and of biological solutions containing sucrose and potassium ions (K+) were investigated by Principal Component Analysis (PGA).

By direct examination of the Mid-Infrared spectra of the biological solutions containing K⁺ ions, no interactions between the cations and sucrose molecules could be observed. However, when the spectral pattern obtained by PCA and which is associated with sucrose, was examined, splitting and shifts in the characteristic absorption bands were observed owing to interactions between sucrose molecules and K⁺ ions. The 997 cm-1 peak which had a visible shoulder at 991 cm-1 and that is observed in pure solutions, was decomposed in the biological solutions into 3 distinct peaks at 1004, 996 and 990 cm-1. The two peaks centered at 1053 cm-1 were split into 3 peaks: 1060, 1051, 1045 cm-1. Hence by PCA, shoulders were characterized in biological solutions and more distinct peaks could be observed. These split and shift phenomena are similar to those obtained when crystalline sugar salts were investigated. This type of interaction, involving potassium ions and sucrose molecules, would be responsible for the storage of this cation which role is essential in plant metabolism.     

Atomic dynamics of tin nanoparticles embedded into porous glass

The method of resonant nuclear inelastic absorption of synchrotron radiation has been used to study the phonon spectrum for tin nanoparticles (with a natural isotope mixture) embedded into a porous glassy (silica) matrix with an average pore diameter of 7 nm in comparison to the analogous spectrum of bulk tin enriched with ¹¹⁹Sn isotope. Differences between the spectra have been observed, which are related to both the dimensional effects and specific structural features of the porous glass-tin nanocomposite. Peculiarities in the dynamics of tin atoms embedded into nanopores of glass are interpreted in terms of a qualitative model of the nanocomposite structure.     

Normal and “Anomalous” isotope shifts of phonon frequencies in mono- and polyisotopic germanium crystals

The shifts of the phonon frequencies in ⁷⁰Ge and ⁷⁴Ge monoisotopic crystals have been studied using inelastic neutron scattering. It has been shown that the frequency shifts for all of the branches are normal, i.e., inversely proportional to √M. At the same time, the gap between acoustic and optical frequencies in monoisotopic crystals appears to be much wider (by about 2 meV in the [111] direction) than that in natural polyisotopic crystals containing “isotopic defects.” In this case, the phonon frequencies undergo “anomalous” shifts; i.e., the oscillation frequency of the heavier isotope is higher than that for the lighter isotope. The effect is in qualitative agreement with old theoretical calculations of the effect of mass defects on the phonon spectra of diatomic lattices.     

Specific effects of a polar solvent in optical absorption spectra of 5,12-tetracenequinone

We have measured the optical absorption spectra of 5,12-tetracenequinone (5,12-naphthacenequinone) in polar protic (methanol) and nonpolar (n-hexane) solvents. It has been shown that shifts of some bands in the polar solvent compared to the nonpolar one are caused by the formation of high hydrogen bonds between methanol molecules and the molecules under study. The occurrence of hydrogen bonds leads to changes in the energy gaps between occupied and unoccupied molecular orbitals of 5,12-tetracenequinone and, as a consequence, to corresponding changes in energies of electronic transitions. Based on analysis of the absorption spectra in different solvents in combination with the data of calculations of electronic spectra and taking into account changes in the orbital pattern under the action of the solvent, we have determined exact electronic configurations of electronically excited singlet states of 5,12-tetracenequinone.     

Vibrational Spectra of 2,2′-Pyridil and 2,2′-Pyridil-18O and Assignment of Infrared and Raman Bands

Abstract

Vibrational spectra of 2,2′-pyridil and 2,2′-pyridil-¹⁸O in the solid state and in solutions have been measured in the Raman (4000–50 cm^?1) and infrared (4000–100 cm^?1). The assignment of the bands observed is performed using the group vibrational concept and isotopic shifts data of the normal modes. The presence of synand anti-phase vibrations of both pyridyl rings is discussed. The results are compared to the corresponding data for some similar molecules.     

Fourier transform infrared spectral study of N,N′-dimethylformamide-water-rhodamine 6G mixture

Infrared absorption spectra of N,N′-dimethyl formamide in the absence and presence of water, rhodamine 6G and water–rhodamine 6G mixture are reported. Assignment of observed bands has been made on the basis of density functional theory calculations and available assignments in the literature. Certain bands show changes in their positions and intensities when water is added to N,N′-dimethylformamide. This is due to hydrogen bonding interaction between these molecules. Similar changes are also observed for dimethylformamide and Rh6G mixture to a lesser extent. The presence of Rh6G in a dimethylformamide–water mixture reverses these spectral changes due to preferential solvation of Cl^? by water molecules. Solvation reduces or nullifies the hydrogen bonding between dimethylformamide and water in the mixture.     

Neutron Scattering and Vibrational Spectra of Molecular Crystals

Infrared and Raman spectra of a number of molecular crystals have been measured for studying molecular vibrations and the intermolecular and intramolecular force fields. The infrared absorption bands arise from interaction of the electric wave with the oscillating dipole moment of the crystal. Raman scattering covers inelastic photon scattering processes and accordingly Raman lines arise from the oscillating polarizability of the crystal. Thus, the vibrational modes observed in infrared absorption or Raman scattering spectra are k = 0 modes, for which translationally equivalent molecules vibrate in phase.     

Calculation and interpretation of IR and resonant raman spectra of 5-halosubstituted uracils

We have used valence optical theory to carry out calculation and analysis of in-plane vibrations and intensities of IR spectra for isolated 5-fluorouracil and 5-bromouracil molecules. We give a complete interpretation of the corresponding bands in the absorption spectra. We have carried out a quantum mechanical calculations of the relative intensities in the resonant Raman spectra of 5-fluorouracil and 5-chlorouracil. The calculated spectra for the molecular models obtained agree quantitatively with the experimental spectra, and reproduce the observed characteristic spectral differences in the series of molecules: uracil, 5-fluorouracil, 5-chlorouracil, and 5-bromouracil. The models obtained for the molecules can be used for calculation and analysis of the spectra of other halosubstituted nucleic acid bases. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 437–442, July–August, 2006.     

Vibrational spectroscopy of interstellar molecules

In this paper we describe how infrared vibrational spectroscopy has been applied in our laboratory to three areas of interest to interstellar chemistry: the origin of the unidentified interstellar infrared emission bands, the depletion of the iron in the interstellar medium, and the fractionation of isotope-bearing molecules in space. In the first area, infrared absorption spectra of polycyclic aromatic hydrocarbons and their ions trapped in cryogenic rare gas matrices have been analyzed and shown to coincide well with the frequencies and relative intensities of the unidentified infrared emission bands. These bands have been observed from many sources in interstellar space, including reflection and planetary nebulae and H II regions, in parts of the Milky Way, as well as other galaxies. In the second area, a free electron laser, with tunable output in the infrared, has been utilized to record resonant multiphoton photodissociation vibrational spectra of various polycyclic aromatic hydrocarbons complexed with Fe⁺ in a Fourier transform ion cyclotron resonance mass spectrometer. Stable complexes found for Fe⁺ and a number of PAHs suggest that iron could be sequestered in such species and that they could function as carriers of the unidentified infrared emission bands. In the third area, the photo-induced ¹³C-isotopic scrambling in the C₃ carbon cluster has been investigated by matrix isolation infrared spectroscopy. Fractionation is shown to arise from small zero-point energy differences in the C₃ isotopomers. A proposed mechanism of isotopic scrambling involving the formation of cyclic C₃ intermediates may be applicable to other species for which isotopic fractionation has also been observed in the ISM.     

Normal Unenhanced Raman Spectra of CO and CH4 Adsorbed on Cobalt(poly)

Abstract

Normal unenhanced Raman spectra (NURS) of low-polarizability CO molecules were observed for the first time on cobalt at R. T. and residual gas pressure. We assign five bands observed between 2030–2130 cm^?1 to linear chemisorbed CO species, while those observed between 1840–2010 cm^?1 have been ascribed to the 2-fold chemisorbed species. The three bands observed between 1740–1830 cm^?1 we believe are due to the 3-fold species. The corresponding fourteen Co-C stretches were observed and assigned. A model based upon electron backdonation is proposed for each of the three structures. NURS were also observed at R. T. for physisorbed CH₄ and assignments are made to the four frequencies of CH_4.