Rotational motion in LiBH4/LiI solid solutions

We investigated the localized rotational diffusion of the (BH(4))(-) anions in LiBH(4)/LiI solid solutions by means of quasielastic and inelastic neutron scattering. The (BH(4))(-) motions are thermally activated and characterized by activation energies in the order of 40 meV. Typical dwell times between jumps are in the picosecond range at temperatures of about 200 K. The motion is dominated by 90° reorientations around the 4-fold symmetry axis of the tetrahedraly shaped (BH(4))(-) ions. As compared to the pure system, the presence of iodide markedly reduces activation energies and increases the rotational frequencies by more than a factor of 100. The addition of iodide lowers the transition temperature, stabilizing the disordered high temperature phase well below room temperature.     

Theoretical and spectroscopic study of infrared spectra of hydrogen-bonded 1-methyluracil crystal and its deuterated derivative

Theoretical simulation of the band shape and fine structure of the N-H(D) stretching band is presented for 1-methyluracil and its deuterated derivative taking into account anharmonic coupling between the high-frequency N-H(D) stretching and the low-frequency N...O stretching vibrations, resonance interaction between two equivalent hydrogen bonds in the dimer, anharmonicity of the potentials for the low-frequency vibrations in the ground and excited state of the N-H(D) stretching mode, Fermi resonance between the N-H(D) stretching and the first overtone of the N-H(D) bending vibrations, and electrical anharmonicity. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman, and low-frequency Raman spectra of the polycrystalline 1-methyluracil have been recorded. The geometry and experimental frequencies are compared with the results of harmonic and anharmonic B3LYP6-311++G(**) calculations.     

Second-order spectrum of water in the K4Fe(CN)6.3H2O crystal

Second-order infrared spectra of the crystal K₄Fe(CN)₆.3H₂O are obtained in the region of 3700–7200 cm^?1 at 90 K. The bands corresponding to overtones and combinations of the stretching and bending modes of the different water molecules are discussed and interpreted. The anharmonicity constants are estimated using the observed frequencies.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Theoretical study of the polarized infrared spectra of the hydrogen bond in 2‐furoic acid crystal dimer

This work presents a theoretical simulation of ν_{O? H} and ν_{O? D} band shapes in the polarized infrared spectra of 2‐furoic acid dimer crystals measured at liquid‐nitrogen temperature. The line shapes are studied theoretically within the framework of the anharmonic couplings between low‐frequency hydrogen‐bond vibrations and degenerate excited states of high‐frequency hydrogen vibrations in hydrogen‐bonded dimers and the anharmonic coupling between the first excited state of the fast mode and the harmonics or band combinations of some low‐frequency bending modes, which lead to Fermi resonances.This approach takes into account the adiabatic approximation, the intrinsic anharmonicity of the low‐frequency mode through a Morse potential, Davydov coupling triggered by resonance exchange between the excited states of the fast modes of the two hydrogen bonds involved in the cyclic dimer, and the direct and indirect damping of the fast‐stretching modes of the hydrogen bonds and of the bending modes. The infrared spectral density was calculated within the linear response theory by Fourier transform of the autocorrelation function of the transition dipole moment operator of the fast mode. Numerical results show that mixing of all these effects allows satisfactory reproduction of the main features of the experimental IR line shapes of crystalline H‐ and D‐bonded 2‐furoic acid at liquid‐nitrogen temperature and for different polarizations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Raman spectra of single H2O molecules isolated in cavities of crystals

The vibrational (Raman) spectra of H₂O molecules isolated in cavities of beryl, cordierite, bikitaite, natrolite, scolecite, lawsonite, and hemimorphite have been measured in the temperature range of 4–295 K. The influence of van der Waals and hydrogen bonds on the values of frequency, intensity, and half-width of stretching and bending modes of H₂O is considered. The spectra of translational vibrations of H₂O molecules in crystal cavities are discussed. For the firsts time, the ratio between the frequencies of translation and stretching vibrations of H₂O and the dependence of frequencies of bending vibrations on the angle H-O-H in H₂O molecule are presented.     

Das Schwingungsspektrum von Magnesium-orthovanadat

The infrared and laser-Raman spectra of crystalline Mg₃(VO₄)₂ are reported and a factor group analysis for the full lattice is presented to support the discussion. The 1,000 to 600 cm^?1 region of the spectrum is essentially related to internal (stretching) modes of the greatly distorted VO₄ tetrahedra, whereas the bands in the low frequency region must be assigned to complex vibrations originating in the interaction of the bending vibrations of the tetrahedral groups with the external modes.     

Vibrational study of (NH4)2HPO4 and (ND4)2DPO4 single crystals. The PO4 ion vibration couplings

The PO₄ internal vibrations have been studied by measuring the polarized infrared (IR) spectra at room temperature (RT) and at low temperature (LT=20K) as well as the polarized Raman (R) spectra. The i.r. dichroism in the (010) plane is investigated in a great range of angles α (0°<α<135°) of the electric vector E with respect to the crystallographic axic c. Some intra ion couplings are inferred. No factor group splitting is observed in the RT IR spectra. However, simultaneously regarding the LT IR spectra and the R spectra promotes an interchain coupling inside the primitive cell. Strong resonance coupling effects are found for the PO₄ stretching modes with the in-plane mode δOH(δOD).     

Vibrational anharmonicity effects in electronic tunneling through molecular bridges

Effects of anharmonic bridge vibrations on electronic tunneling in donor-bridge-acceptor complexes are studied using a model of anharmonic bridge vibration coupled nonlinearly to an electronic degree of freedom. An anharmonicity parameter is introduced, enabling to reproduce the standard harmonic model with linear coupling as a limiting case. The frequency of electronic tunneling oscillations between the donor and acceptor sites is shown to be sensitive to the nuclear anharmonicity, where stretching and compression modes have an opposite effect on the electronic frequency. This phenomenon, that cannot be accounted for within the harmonic approximation, is analyzed and explained.     

Neutron inelastic scattering spectra of strongly hydrogen bonded acid oxalates NaHC2O4, KHC2O4 and LiHC2O4

Neutron inelastic scattering spectra of NaHC₂O₄, KHC₂O₄ crystals at 80 K have been recorded in the 2200-200 cm^?1 range. The lithium acid salt was also studied at different temperatures. NIS spectra are compared to the corresponding infrared and Raman spectra and an assignment is proposed. Two strong bands near 1500 and 1100 cm^?1 are assigned to δ(OH) and γ(OH) vibrations, respectively, while five weak bands below 900 cm^?1 are associated with skeletal modes, mainly bending vibrations. The OH stretching vibration is not observed and is believed to be hidden by other bands; the peak intensity must be low because of its band width which is of the order of a few hundreds wavenumbers.     

Infrared spectra of the Cl- -C2H4 and Br- -C2H4 anion dimers

Infrared spectra of mass-selected Cl- -C2H4 and Br- -C2H4 complexes are recorded in the vicinity of the ethylene CH stretching vibrations (2700-3300 cm(-1) using vibrational predissociation spectroscopy. Spectra of both complexes exhibit 6 prominent peaks in the CH stretch region. Comparison with calculated frequencies reveal that the 4 higher frequency bands are associated with CH stretching modes of the C2H4 subunit, while the 2 weaker bands are assigned as overtone or combinations bands gaining intensity through interaction with the CH stretches. Ab initio calculations at the MP2/aug-cc-pVDZ level suggest that C2H4 preferentially forms a single linear H-bond with Cl- and Br- although a planar bifurcated configuration lies only slightly higher in energy (by 110 and 16 cm(-1), respectively). One-dimensional potential energy curves describing the in-plane intermolecular bending motion are developed which are used to determine the corresponding vibrational energies and wavefunctions. Experimental and theoretical results suggest that in their ground vibrational state the Cl- -C2H4 and Br- -C2H4 complexes are localized in the single H-bonded configuration, but that with the addition of modest amounts of internal energy, the in-plane bending wavefunction also has significant amplitude in the bifurcated structure.     

Raman spectroscopy of uranyl rare earth carbonate kamotoite-(Y)

Raman spectroscopy at 298 and 77K has been used to study the mineral kamotoite-(Y), a uranyl rare earth carbonate mineral of formula Y(2)(UO(2))(4)(CO(3))(3)(OH)(8).10-11H(2)O. The mineral is characterised by two Raman bands at 1130.9 and 1124.6 cm(-1) assigned to the nu(1) symmetric stretching mode of the (CO(3))(2-) units, while those at 1170.4 and 862.3 cm(-1) (77K) to the deltaU-OH bending vibrations. The assignment of the two bands at 814.7 and 809.6 cm(-1) is difficult because of the potential overlap between the symmetric stretching modes of the (UO(2))(2+) units and the nu(2) bending modes of the (CO(3))(2-) units. Only a single band is observed in the 77K spectrum at 811.6 cm(-1). One possible assignment is that the band at 814.7 cm(-1) is attributable to the nu(1) symmetric stretching mode of the (UO(2))(2+) units and the second band at 809.6 cm(-1) is due to the nu(2) bending modes of the (CO(3))(2-) units. Bands observed at 584 and 547.3 cm(-1) are attributed to water librational modes. An intense band at 417.7 cm(-1) resolved into two components at 422.0 and 416.6 cm(-1) in the 77K spectrum is assigned to an Y(2)O(2) stretching vibration. Bands at 336.3, 286.4 and 231.6 cm(-1) are assigned to the nu(2) (UO(2))(2+) bending modes. U-O bond lengths in uranyl are calculated from the wavenumbers of the uranyl symmetric stretching vibrations. The presence of symmetrically distinct uranyl and carbonate units in the crystal structure of kamotoite-(Y) is assumed. Hydrogen-bonding network related to the presence of water molecules and hydroxyls is shortly discussed.     

Multipole induced splitting of metal-cage vibrations in crystalline endohedral D2d-M2@C84 dimetallofullerenes

Metal-carbon cage vibrations of crystalline endohedral D2d-M2@C84 (M=Sc,Y,Dy) dimetallofullerenes were analyzed by temperature dependent Raman scattering and a dynamical force field model. Three groups of metal-carbon cage modes were found at energies of 35-200 cm(-1) and assigned to metal-cage stretching and deformation vibrations. They exhibit a textbook example for the splitting of molecular vibrations in a crystal field. Induced dipole-dipole and quadrupole-quadrupole interactions account quantitatively for the observed mode splitting. Based on the metal-cage vibrational structure it is demonstrated that D2d-Y2@C84 dimetallofullerene retains a monoclinic crystal structure up to 550 K and undergoes a transition from a disordered to an ordered orientational state at a temperature of approximately 150 K.     

Theoretical modeling of infrared spectra of benzoic acid and its deuterated derivative

Theoretical simulation of the ν_s stretching band is presented for benzoic acid and its OD derivative at 300 K. The simulation takes into account an adiabatic coupling between the high-frequency O–H(D) stretching and the low-frequency intermolecular OO stretching modes, linear and quadratic distortions of the potential energy for the low-frequency vibrations in the excited state of the O–H(D) stretching vibration, resonance interaction between the two hydrogen bonds in the dimer, and Fermi resonance between the fundamental ν OH(D) stretching and the overtone of the δ O–H(D) bending vibrations.

Infrared, far-infarared, Raman and low-frequency Raman spectra of the polycrystalline benzoic acid and its deuterated form have been measured. The geometry and experimental frequencies are compared with the results of our B3LYP/6-311++G** and B3LYP/cc-pVTZ calculations.     

Fermi resonances of borohydrides in a crystalline environment of alkali metals

Vibrational spectra of BH(4)(-) and its isotopic analogues in a crystalline environment of alkali metals cations (K(+), Rb(+), Cs(+)) have been investigated beyond the harmonic approximation using a variational approach supported by computations of B3LYP type anharmonic force fields. From the comparison of the observed and simulated IR spectra, the influence of the anharmonic couplings on the band position and on the relative intensity of the allowed vibrational transitions is discussed. Here, the effect of the crystalline environment induces a blue shift of about 50 and 100 cm(-1) respectively for the bending and stretching modes of BH(4)(-). Furthermore, anharmonic effects, which are exclusively well reproduced by a variational approach, are needed to yield reliable positions and relative amplitudes of IR allowed combination and overtone transitions. This leads to theoretical results fitting their experimental counterpart between 6 and 30 cm(-1) in the investigated series.     

Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives

The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Moller-Plesset second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C(infinity v) symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.     

Laser Raman and infrared spectral studies of dl-phenylalaninium nitrate

The vibrational band assignments of dl-phenylalaninium nitrate in the crystalline state are made by recording the infrared and Raman spectra at room temperature. The presence of carbonyl (C=O) group has been identified. The prominent marker bands of the aromatic amino acid phenylalanine have been observed and the various modes of vibration have been assigned. The extensive intermolecular hydrogen bonding in the crystal has been identified by the shifting of bands due to the stretching and bending modes of the various functional groups. The nitrate group forms the anion. The stretching and bending wave numbers of the NO(3)(-) anion are different from those observed for free ion state and the degenerating mode of vibrations is also lifted. These reveal that the crystalline field has influenced the symmetry of the nitrate ion.     

IR, 1H NMR, mass, XRD and TGA/DTA investigations on the ciprofloxacin/iodine charge-transfer complex

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)·2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H?O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases.     

Hydrogen bonding: How much anharmonicity?

In moderately strong hydrogen bonds, hydrogen bond formation increases the anharmonicity constant of the high frequency stretching vibration, significantly but not dramatically. This increase tends to increase with the strength of the hydrogen bond. The main cause of the fine structure and breadth of this band is, however, coupling with both the low frequency stretching and bending vibrations of the bridge, despite the smallness of the coupling constants. Second–order perturbation theory is sufficient to interpret the observed frequencies in the case of moderately strong hydrogen bonds. HCNHF, O–H:O, O–H:N, and N–H:N hydrogen bonds are considered.     

Vibrations de valence C?H/C?D fondamentales et harmoniques de dérivés halogénés du méthane et du deutériométhane

The fundamentals and overtones of the C? H stretching vibrations of a number of halogenated methanes and deuteriomethanes are compared with a hypothetical model consisting of isolated groups. The anharmonicity constants are evaluated and lie between ?20 cm^?1 and ?130 cm^?1 for the C? H and C? D stretching vibrations. The value of the anharmonicity constant for a coupling between two different modes of vibration is always greater (in absolute numbers) than its value for an overtone of one frequency. The constant is larger for a symmetric mode than for an asymmetric mode in the case of a C? H vibration; the contrary is true for a C? D bond. Complex interactions between different vibrations often strongly modify the spectra of the overtones. It is shown, however, that the conception of an isolated group is helpful for evaluating the spectra of these substances.