Temperature-dependent vibrational spectroscopic studies of pure and gold nanoparticles dispersed 4-n-Hexyloxy-4’-cyanobiphenyls

Raman spectra of pure and 2 wt.% gold nanoparticles (GNPs) dispersed liquid crystalline compound 4-n-Hexyloxy-4?- cyanobiphenyls (6OCB) has been recorded as a function of temperature from room temperature (solid crystal) to 80°C (isotropic liquid) in the spectral region of 500–2500 cm^?1. The variation of Raman spectral parameters (peak positions and line width) with temperature is used to explain the changes in molecular alignment and its effect on inter-/intra-molecular interactions at crystal-Nematic (K-N) transition. To understand the change in molecular structure during phase transition and on account of dispersion of gold nanoparticles in pure liquid crystal more precisely, two spectral regions 1000–1500 cm^?1 and 1500–2400 cm^?1 have been selected separately. From the detailed study, it is concluded that increased orientational/vibrational freedom of the molecules as well as delocalisation of electron clouds results in the spectral anomalies at K-N transition. The geometrical structure of 6OCB was optimised using density functional theory (DFT) and theoretical Raman spectra have been obtained for comparison with experimental spectra. The tentative assignment of vibrational modes observed in our region of study was calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) calculation.     

Time‐Resolved FTIR Emission Spectroscopy of Transient Radicals

Fourier Transform spectroscopy with 10^?8 second time resolution for recording IR emission spectra has been developed as an efficient means for detecting previously unknown vibrational modes of transient radicals. 193 nm photodissociation of a precursor molecule is used to generate vibrationally excited radicals, from which IR emission is recorded with time and spectral resolution. Assignment of the spectra is performed using information obtained through multiple precursors, isotopic substitution, time dependence of emission intensity, theoretical calculations, and 2‐dimensional cross‐spectra correlation analysis. The radicals vinyl, cyanovinyl, and OCCN have been studied with many vibrational modes identified.     

Time resolved fluorescence of anthracene in mixed crystals at 2K

An optical Kerr shuttered spectrograph has been used to time resolve the spontaneous fluorescence of aromatic mixed crystal systems at low temperature with moderate resolution. Transient effects on the fluorescence of anthracene in naphthalene excited with 614 cm^?1 vibrational excess energy in ¹B_2u have been observed that may signal measurable vibrational relaxation pathways. A model consistent with these observations is presented: it implicates a strong interaction between the intramolecular Franck—Condon and non-Franck—Condon modes in the relaxation process for specific excitation in the region of large excess lattice energy. Examination of the fluorescence for several aromatic systems integrated over the interval 0 to 30 ps following excitation high in the S₁ vibrational manifold failed to reveal evidence of non-Boltzmann vibrational distributions, although other largely unexplained effects have been observed.     

Vibrational spectra of sodium gadolinium tungstate NaGd(WO4)2 single crystals: Observation of spatial dispersion

Room temperature polarized Raman scattering and infrared reflectance spectra of a NaGd(WO₄)₂ single crystal have been measured. The IR spectra interpretation was aided by a Kramers-Krönig analysis, and fitted to the independent oscillator model. All 13 theoretically expected Raman-active bands have been identified and assigned, as well as 7 out of 8 expected IR active bands. Splitting of bands in both Raman and IR clearly indicates a lowering of the crystal symmetry due to occupation disorder in the 4a site, that randomly accommodates either an Na⁺ or a Gd³⁺ ion. The reflectance IR spectra reveal a spatial dispersion, namely a dependence of the transverse optical (TO) polariton frequencies, on the propagation direction in the crystal. The crystal vibrational modes are correlated to the internal modes of the tungstate group WO₄^2?, and to the internal modes of the molecular skeleton. A detailed correlation map of the symmetry analysis is presented.     

The Raman active internal vibrational modes of potassium nitrate

The Raman active internal vibrational modes of single crystal orthorhombic potassium nitrate have been studied in various polarizations. The full multiplet structure predicted by factor group analysis for the v₂ and v₃ regions has been observed for the first time. The expected site group splitting of the v₄ mode was not observed and can be assumed to be less than 0.5 cm^?1.     

Spectra and structure of phosphorus-boron compounds: VII. Vibrational analysis of solid phosphine-borane

The infrared (70–2700 cm^?) and Raman (25–2500 cm^?1) spectra of H₃PBH₃, H₃PBD₃, D₃PBH₃ and D₃PBD₃ in the solid state at ?196 °C have been recorded. The shift associated with the boron-10 and boron-11 isotopes was observed for the P-B stretching motion. A complete vibrational assignment is proposed and a normal coordinate calculation utilizing a valence force field model has been carried out. The force constant of 1.97 mdyn Å^?1 for the phosphorus-boron stretching mode is consistent with the relatively long phosphorus-boron bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. None of the E modes for the “free” molecule were found to be split. The number of observed lattice modes is not consistent with the crystal structure previously reported for this molecule. A possible explanation is discussed.     

The Raman spectra of ferrocene-b10 and -d10: librational modes and comments upon previous polarization data

The librational modes of ferrocene-h₁₀ and -d₁₀ have been observed near 62 cm^?1 (-h₁₀) and 40, 52 and 60 cm^?1 (-d₁₀). The polarization measurements at low temperatures can give no useful information concerning the vibrational assignment until the low temperature crystal structure is completely determined.     

Isotopic mixed crystal exciton spectra in the far infrared: Naphthalene

The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene-h₈ and d₈ were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B_3u, A_u and B_1u vibrational exciton bands were found to be in the separated band limit. The lowest energy B_3u “butterfly” mode with its large (15 cm^?1) exciton splitting was found to agree well with CPA calculations of mixed crystal spectra. A peak at 185 cm^?1 was also assigned as a peak in the vibrational exciton density-of-states of the B_3u mode.     

Hexamminmetall(III)-hexachlorochromate(III): Darstellung,Kristallgitter und Spektren

Hexammine-metal(III) hexachlorochromates(III). Preparation, crystal lattic and spectra The preparation of [Me(NH₃)₆]CrCl₆ with Me = Co and Rh from aqueous solutions and with Me = Co, Cr and Rh by thermal dehydratation is given. The crystal structure of these compounds is T_h⁶? Pa3, Z = 4. The absorption spectrum shows the two known spin allowed bands at 13300 and 1890C cm^?1. Some weak vibronic absorptions are observed from 13870 cm^?1 to 15130 cm^?1. The vibrational spectrum of CrCl₆^2? has been completed by the measurement of the RAMAN spectrum, the IR spectra have been reinvestigated. The vibrational spectra confirm the nearly undisturbed octahedral symmetry of the hexahalogenometallate anion which has previously been observed for similar compounds.     

Raman scattering study of toluene vibrational relaxation in benzene-toluene liquid system

The polarizes and depolarized profiles of the 520 cm^?1 Raman line of toluene in benzene solutions have been measured as a function of concentration. The vibrational correlation functions were obtained by Fourier inversion of Raman band contours. The concentration dependence of the experimental vibrational correlation time has been compared with that computed from the Fischer-Laubereau vibrational dephasing model modified for use in binary mixtures.     

Molecular Vibronic Structures of HDITC in Solutions Studied by Femtosecond Wavelength-Resolved Pump-Probe Spectroscopy

Wavelength-resolved pump-probe measurements using 11 fs duration pulses were performed to study the vibronic structures of HDITC, a cyanine dye, in ethylene glycol. Ten vibrational modes were observed in the forms of quantum beats. The frequencies of these ten vibrational modes ranged from 135 cm^?1 to 1300 cm^?1. The relative potential displacements along these ten vibrational coordinates were estimated by comparison with theoretical calculations.     

Microstrain investigation of polyethylene

The small-strain mechanical behavior of crystalline polyethylene has been studied by using a microstrain technique with strain resolution on the order of 10^?6. The strain rate was varied from 10^?6 to 10^?4 sec.^?1, and a temperature range of 17–28°C. was investigated. A strong dependence on strain rate and temperature has been observed for the following parameters which characterize the mechanical response of polyethylene in the microstrain region: the initial modulus of the stress–strain curve, the deviation in strain from ideal linear elastic behavior at a given stress amplitude, and the energy dissipated in a deformation cycle. The Young's moduli that were observed by means of tensile tests in the microstrain region were only about 20% lower than the values reported in other investigations at kilocycle and megacycle frequencies. The experimental method made it possible to isolate a deformation process which was attributed to a crystallographic shear mechanism corresponding to a yield point of 27 psi. This shear mechanism is discussed in terms of the various shear processes, such as slip, twinning, and the orthorhombic–monoclinic phase change.     

Low frequency raman spectra of isotopic mixed benzophenone crystals

In this paper, we present an experimental study of vibrational lattice modes in isotopic mixed crystals of benzophenone-h₁₀ and -d₁₀. Our results are discussed using theoretical and experimental data concerning other molecular isotopic mixed crystals. The spectra show two regions; in the first (ν < 100 cm^?1) we did not observe an interaction between the various vibrational lattice bands; in the second region (ν > 100 cm^?1), the interaction appears clearly. The 111.5 cm^?1 and 73 cm^?1 torsional modes of benzophenone-h₁₀ have the same behaviour as the external modes throughout the whole concentration range (0–100% of benzophenone-d₁₀).     

Exploring the Vibrational Side of Spin‐Phonon Coupling in Single‐Molecule Magnets via 161Dy Nuclear Resonance Vibrational Spectroscopy

Synchrotron‐based nuclear resonance vibrational spectroscopy (NRVS) using the Mössbauer isotope ¹⁶¹Dy has been employed for the first time to study the vibrational properties of a single‐molecule magnet (SMM) incorporating Dy^III, namely [Dy(Cy₃PO)₂(H₂O)₅]Br₃?2 (Cy₃PO)?2 H₂O ?2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the Dy^III ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that ¹⁶¹Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.     

Vibrational relaxation in liquid diethylamine

Two types of time resolved experiments have been performed on the intermediate sized polyatomic molecule diethylamine, in the liquid phase, in order to elucidate the pathway for vibrational relaxation of the ν = 3 level of the NH stretching mode, which has 9420 cm^?1 of energy. Both techniques had calibrated absolute sensitivities and were specific for vibrational modes of ca. 3000 cm^?1, yet with neither were transient populations in such modes observable. It is inferred that population relaxation in this highly excited room temperature system proceeds on the subpicosecond time scale to lower lying levels. The importance of intramolecular channels for this decay is suggested.     

OH stretching frequencies of solid hydroxides and of free OH− ions

The vibrational frequency of free OH^? ions, which cannot be directly measured, has been claimed to be 3700 cm^?1. In solid hydroxides the OH stretching frequency has been found in the range from 3690 to 3100 cm^?1. The decrease of the vibrational frequency has been interpreted to be caused by hydrogen bridges or the increase of the metal oxygen bond strength. We suggest an alternative explanation. The vibrational frequency of unperturbed OH^? ions is 3570 ± 10 cm^?1. In ionic hydroxides this frequency is increased due to repulsion effects of the lattice or decreased if hydrogen bonds are present, to a large extent (up to 400 cm^?1) in the case of common OH^?….X bridges and only up to 70 cm^?1 in the case of XH….OH^? bonds.     

Raman spectroscopy of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines were synthesized, they exhibited a nematic phase. The temperature dependence of their Raman spectra has been observed in the spectral range 900–1800?cm^?1. Some Raman bands show a marked change in their intensity and frequency through the phase transition from crystalline solid to nematic. These bands are ascribed to the vibrational modes related to the core part of the molecule. Such behaviour can be explained by the change of molecular conformation related to the core. Some members of these series exhibited photochromism in the solid state.     

Raman spectra of 3-methyl-4-nitropyridine-N-oxide single crystal

A Raman study of 3-methyl-4-nitropyridine-N-oxide single crystal (3M4NPO) has been performed at 78 K in the range 10–3500 cm⁻¹. The symmetry analysis of the vibrational modes of 3M4NPO is given. The assignments are presented for internal and external modes. The results of the Raman spectra exhibit the spectroscopic proofs of hydrogen bonds in the crystal.     

Calculated lifetime and decay mechanism of the 991 cm−1 mode in crystalline benzene at 1.6 K

The lifetime of the 991 cm^?1 Ag mode in benzene crystal at 1.6 K has been calculated in good agreement with the experimental value. The main decay mechanism has been shown to consist of a three-phonon scattering involving the ν₁₀ 860 cm^?1 e_2g internal vibration and high-frequency lattice modes.     

The vibrational energy manifold of the lowest lying bending mode of tricarbon oxide sulfide,OCCCS,as determined by relative intensity measurements

The determination of a precise vibrational energy level scheme for the two-dimensional bending mode of tricarbon oxide sulfide (3-thioxo-1,2-propadiene-1-one), OCCCS, has been carried out by relative intensity measurements of rotational transitions up to the seventh excited vibrational state of ν₇. The harmonic wavenumber ω₇ was determined to be 84.50 ± 0.63 cm^?1 while the anharmonicity constant χ₇₇ was found to be ?0.62 ± 0.11 cm^?1, respectively. A linear dependence of the expectation value of the electric dipole moment on the vibrational quantum number υ₇ was found. All results confirm that in O CCCS the potential function describing the two-dimensional oscillator of ν₇ is very harmonic without a perturbing barrier to linearity as was found in the case of OCCCO.