Raman and infrared vibrational modes of tricosane paraffin under high pressure

This paper reports an experimental study about the pressure dependence of the vibrational modes of tricosane paraffin (C₂₃H₄₈) investigated by in situ Raman and infrared spectroscopy in a diamond anvil cell (DAC). The main vibrational bands were followed up to 11 GPa and the observed behavior indicated a conformational disorder induced by pressure, corresponding to a transition from ordered to disordered state of the linear chains from 2 to 5 GPa followed by a transition to an amorphous state under pressure above 5 GPa. However, this behavior was reversible after compression–decompression cycle showing that this linear compound was structurally and chemically stable up to 11 GPa at room temperature.     

Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.     

The vibrational analysis of some potassium salts

The IR, far-IR and Raman spectra of products with general formula X—COOK (X = —CONH₂, —CONHCH₃ and —CSNH₂) and the N-deuterated derivatives have been recorded, the fundamental vibrational frequencies assigned, and a valence force field calculated.     

Raman spectra of vibrational and librational modes in methane clathrate hydrates using density functional theory

The sI type methane clathrate hydrate lattice is formed during the process of nucleation where methane gas molecules are encapsulated in the form of dodecahedron (5(12)CH(4)) and tetrakaidecahedron (5(12)6(2)CH(4)) water cages. The characterization of change in the vibrational modes which occur on the encapsulation of CH(4) in these cages plays a key role in understanding the formation of these cages and subsequent growth to form the hydrate lattice. In this present work, we have chosen the density functional theory (DFT) using the dispersion corrected B97-D functional to characterize the Raman frequency vibrational modes of CH(4) and surrounding water molecules in these cages. The symmetric and asymmetric C-H stretch in the 5(12)CH(4) cage is found to shift to higher frequency due to dispersion interaction of the encapsulated CH(4) molecule with the water molecules of the cages. However, the symmetric and asymmetric O-H stretch of water molecules in 5(12)CH(4) and 5(12)6(2)CH(4) cages are shifted towards lower frequency due to hydrogen bonding, and interactions with the encapsulated CH(4) molecules. The CH(4) bending modes in the 5(12)CH(4) and 5(12)6(2)CH(4) cages are blueshifted, though the magnitude of the shifts is lower compared to modes in the high frequency region which suggests bending modes are less affected on encapsulation of CH(4). The low frequency librational modes which are collective motion of the water molecules and CH(4) in these cages show a broad range of frequencies which suggests that these modes largely contribute to the formation of the hydrate lattice.     

Structure and vibrational modes of AgI-doped AsSe glasses: Raman scattering and ab initio calculations

We report an investigation of the structure and vibrational modes of (AgI)_x (AsSe)_100−x, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As₄Se_n, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As₄Se_n molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe_mI_3−m provided useful information augmenting the interpretation of the Raman spectra.     

The vibrational Raman spectra of selenium trioxide ag

The vibrational Raman spectra of selenium trioxide have been observed in the solid and vapour phases for the same sample. The spectrum of the vapour phase, which essentially arises from the monomeric species SeO₃, has provided for the first time values of the Raman-active ν₁, ν₃ and ν₄ wavenumbers of SeO₃. The spectrum of the solid phase represents an improvement on previous work and has enabled a partial assignment of the tetrameric species (SeO₃)₄ to be made.     

Theoretical differential Raman scattering cross-sections of totally-symmetric vibrational modes of free pyridine and pyridine-metal cluster complexes

The differential Raman scattering cross-sections of totally-symmetric vibrational modes for pyridine and pyridine-metal clusters have been calculated by using ab initio and density functional methods. The results are compared with experimental data and a good agreement is obtained. In particular, we can theoretically reproduce the significant changes in the relative Raman intensities of the nu(12) mode in pyridine-metal cluster complexes. We focus on two mechanisms for these Raman intensities changes: (1) the chemical interaction between the pyridine and the metal clusters; and (2) the charge transfer mechanism. For the pyridine-silver cluster complexes, we find that due to the weak bonding, the chemical interaction does not influence the relative intensities of the Raman peaks of the nu(1) and nu(12) modes. However, in the case where the copper or the gold clusters are attached to pyridine, the intensity of the band of the nu(12) mode is weakened significantly. We also find that the charge transfer mechanism increases the asymmetry of the bands of the nu(1) and nu(12) modes on all three metals.     

A new way of analyzing vibrational spectra. I. Derivation of adiabatic internal modes

A new way of analyzing measured or calculated vibrational spectra in terms of internal vibrational modes associated with the internal parameters used to describe geometry and conformation of a molecule is described. The internal modes are determined by solving the Euler–Lagrange equations for molecular fragments ϕ_n described by internal parameters ζ_n. An internal mode is localized in a molecular fragment by describing the rest of the molecule as a collection of massless points that just define molecular geometry. Alternatively, one can consider the new fragment motions as motions that are obtained after relaxing all parts of the vibrating molecule but the fragment under consideration. Because of this property, the internal modes are called adiabatic internal modes, and the associated force constants k_a, adiabatic force constants. Minimization of the kinetic energy of the vibrating fragment ϕ_n yields the adiabatic mass m_a (corresponding to 1/G_nn of Wilson's G matrix) and, by this, adiabatic frequencies ω_a. Adiabatic modes are perfectly suited to analyze and understand the vibrational spectra of a molecule in terms of internal parameter modes in the same way as one understands molecular geometry in terms of internal coordinates. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67 : 1–9, 1998     

Relating normal vibrational modes to local vibrational modes with the help of an adiabatic connection scheme

Information on the electronic structure of a molecule and its chemical bonds is encoded in the molecular normal vibrational modes. However, normal vibrational modes result from a coupling of local vibrational modes, which means that only the latter can provide detailed insight into bonding and other structural features. In this work, it is proven that the adiabatic internal coordinate vibrational modes of Konkoli and Cremer [Int. J. Quantum Chem. 67, 29 (1998)] represent a unique set of local modes that is directly related to the normal vibrational modes. The missing link between these two sets of modes are the compliance constants of Decius, which turn out to be the reciprocals of the local mode force constants of Konkoli and Cremer. Using the compliance constants matrix, the local mode frequencies of any molecule can be converted into its normal mode frequencies with the help of an adiabatic connection scheme that defines the coupling of the local modes in terms of coupling frequencies and reveals how avoided crossings between the local modes lead to changes in the character of the normal modes.     

Vibrational amplitude profile of molecular vibrational modes for vibrational mode assignment

Ultrashort pulse lasers with 6- and 20-fs durations were utilized for phthalocyanine thin film sample to induce several vibrational modes and vibration amplitude spectra were determined by multi-wavelength measurement technique. From the spectra we could identify the electronic states, which couple to two vibrational modes with frequencies of 670 and 750 cm⁻¹. It was shown that the vibrational amplitude profile obtained by the method can be used for providing information for the assignment of the vibrational mode.     

Modelling vibrational modes in diacetylene polymers

High-frequency vibrational modes in polydiacetylene polymers have been simulated using a simple point-mass and harmonic- force-constant model. Excellent agreement has been found between the frequencies of these modes and those observed in resonant Raman scattering from crystals of polydiacetylene polymers with four radically different sidegroups. The atomic displacement vectors for each mode have also been calculated and related to backbone-sidegroup interactions on the polymer chain.     

The vibrational Raman spectra of C60 and C70

Vibrational Raman spectra have been obtained at 1 cm⁻¹ resolution, for C₆₀ and C₇₀. For C₆₀ the positions of the bands were in good agreement with theoretical predictions. For C₇₀ 27 bands were observed out of the total of 53 that were theoretically predicted. These data will permit refinement of calculations of vibrational lines appropriate to closed-cage carbon clusters. The technique for producing appreciable quantities of high purity C₇₀ is described.     

Ab-initio calculations of Raman, IR-active vibrational modes in isotopically modified B12 icosahedral clusters

Computational calculations of Becke's three-parameter hybrid method using the LYP correlation functional (B3LYP) have been performed on (B₁₂H₁₂)²⁻ dodecaborane anions with different boron isotopic compositions. This was done in order to investigate isotopic dependence of vibrational spectral properties of B₁₂ icosahedra, and for comparison of the optical vibrational properties of the icosahedral molecule with the characteristics of inter- or intra-icosahedral optical phonon vibrational modes in boron-rich crystals.     

Symmetry properties of vibrational modes in mesoporphyrin IX dimethyl ester investigated by polarization-sensitive resonance Raman and CARS spectroscopy

The symmetry properties of selected vibrational modes of mesoporphyrin IX dimethyl ester (MP-IX-DME) in solution are investigated under different electronic resonance conditions. The Raman band parameters of the macrocycle modes nu(2), nu(10), nu(11), and nu(19) are determined from a quantitative analysis of polarized spontaneous resonance Raman (RR) and polarization-sensitive (PS) multiplex coherent anti-Stokes Raman scattering (CARS) spectra obtained with pre-resonant B band and resonant Qx band excitation, respectively. Additionally, the molecular geometry and the vibrational modes of MP-IX-DME are calculated by employing density functional theory (DFT) on the B3LYP/6-31G(d) level. Both the DFT-derived structure and the Raman spectroscopic parameters of MP-IX-DME indicate minor deviations from an ideal D2h macrocycle symmetry. To assess the influence of the beta substitution pattern on the in-plane symmetry, calculated normal-mode vectors and several experimentally detected parameters, such as peak positions, depolarization ratios, and coherent phases, are analyzed. The effects of the macrocycle substitution pattern are different for the selected vibrational modes: nu(2) in particular is very sensitive to subtle perturbations of the in-plane symmetry. The considerable activity of totally symmetric vibrations observed in the PS CARS spectra of MP-IX-DME and the correlation of mode symmetries with coherent phases confirm earlier PS CARS results on octaethylporphine (OEP) acquired under the same electronic resonance conditions.     

The formation and decay of radicals in potassium nitrate

The buildup kinetics of the radicals produced by irradiation of potassium nitrate at 77 K over a wide dose range and the postradiation transformations of paramagnetic centers over the temperature range 38-401 K were studied. The low-temperature limit for the radical decay rate was determined. The specific features of the radical buildup kinetics were associated with the two factors, the restrictions for hole and electron trapping sites and the set of recombination reactions including tunneling recombination of trapped charges. The parameters of tunneling reactions of radical recombination were evaluated, which appeared to be of the same order of magnitude as those for glassy materials     

Vibrational assignment of the Raman active modes of 1,10-phenanthroline-5,6-dione using DFT calculations

A complete assignment of the Raman active modes of 1,10-phenanthroline-5,6-dione in the 100-4000 cm(-1) spectral region is reported. Intense well resolved spectra of solid phendione with high S/N are reported. Assignment of the normal modes with appropriate symmetry representation symbols was achieved by employing density functional theory calculations. Our calculations were modeled on results previously reported for phenanthroline. Results of the B3LYP calculations were consistent and established that phendione possess sixty fundamentals.     

Phase transitions in potassium nitrate

It is shown that the heat of transition of the phase change II → I at 129° on heating KNO₃ is dependent on the thermal history of the sample, since it involves two steps, viz., II→ III and III→ I at 2° interval. During cooling, the latter step is fast and truly reversible, though with a temperature hysteresis. The former step is sluggish and is dependent both on temperature and time. Our results indicate that KNO₃ can be used for calibration purpose only if the material has not been heated beyond 128° in the immediately preceding three hours.     

Local normal modes and vibrational adiabatic potentials

Local normal-mode analysis for a collinear potential energy surface generates a system of curvilinear coordinates, which are orthogonal in the mass-skewed system. The motion is locally separable in these coordinates. We compare the utility of one of the normal modes as a transversal-vibration coordinate, with the conventional choice of the direction perpendicular to the reaction coordinate in the mass-skewed system. The comparison is done for two commonly used reaction coordinates: BEBO and the steepest-descent path. Results differ for different choices of directions and reaction coordinates. Future work should concentrate on a choice of a reaction coordinate which is itself one of the normal modes.     

The structure and the Raman vibrational spectrum of the beryllium aquacation

The experimental Raman vibrational spectrum of the 5.94 m water solution of the beryllium(II) chloride has been acquired. Theoretical frequencies, infrared and Raman intensities of the vibrational spectrum of the beryllium cation tetrahydrate have been calculated by means of quantum chemical approach. The peaks of the experimental spectrum have been assigned on the basis of the results of the quantum-chemical calculations. It has been shown that the hydrating surrounding of the aquacation increases effectively the frequency of the beryllium-oxygen stretching vibration by 16% in comparison with the free complex.     

Relation between s-polarized and p-polarized internal reflection spectra: application for the spectral resolution of perpendicular vibrational modes

The orientation of chemical bonds in thin films is commonly probed with polarized internal reflection Fourier transform infrared spectroscopy. Here we demonstrate how the internal reflection spectra obtained using s-polarized light are related with the corresponding p-polarized spectra. The relation between s- and p-polarized internal reflection spectra is applied to resolve the absorption bands of vibrational modes with components oriented perpendicular to the substrate. This is successfully demonstrated using Langmuir-Blodgett films containing smectite clay minerals and a surfactant deposited on ZnSe and Ge internal reflection elements.