Tuning of phonon anharmonicity in pyrochlore titanates: temperature‐dependent Raman studies of Sm2Ti2‐xZrxO7 (x=0, 1/2, 3/4, and 2) and stuffed spin‐ice Ho2 + xTi2 − xO7 − x/2 (x=0, 1/3, and 2/3)

Anomalous temperature dependence of Raman phonon wavenumbers attributed to phonon–phonon anharmonic interactions has been studied in two different families of pyrochlore titanates. We bring out the role of the ionic size of titanium and the inherent vacancies of pyrochlore in these anomalies by studying the effect of replacement of Ti^{4 +} by Zr^{4 +} in Sm₂Ti₂O₇ and by stuffing Ho^{3 +} in place of Ti^{4 +} in Ho₂Ti₂O₇ with appropriate oxygen stoichiometry. Our results show that an increase in the concentration of the larger ion, i.e. Zr^{4 +} or Ho^{3 +}, reduces the phonon anomalies, thus implying a decrease in the phonon–phonon anharmonic interactions. In addition, we find signatures of coupling between a phonon and crystal field transition in Sm₂Ti₂O₇, manifested as an unusual increase in the phonon intensity with increasing temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF)2X (X = ReO4, ClO4) with regular organic stacks

A novel selective synthesis of the unsymmetrically substituted tetrathiafulvalene dimethyltrimethylene‐tetrathiafulvalene (DMtTTF) is described together with its electrocrystallization to the known conducting mixed‐valence ClO₄^– and ReO₄^– salts. Infrared (IR) and Raman spectra of the two isostructural quasi‐one‐dimensional cation radical salts (DMtTTF)₂X (X = ReO₄^–, ClO₄^–) are investigated as a function of temperature (T = 5–300 K). At ambient temperature, these salts show metallic‐like properties and below T_ρ = 100–150 K, they undergo a smeared transition to semiconducting state. To study this charge localization, we measured temperature dependence of polarized IR reflectance spectra (700–16 000 cm^–1) and Raman spectra (150–3500 cm^–1, excitation λ = 632.8 nm) of single crystals. For both compounds, the Raman data and especially the bands related to the C=C stretching vibration of the DMtTTF molecule show that the charge distribution on molecules is uniform down to the lowest temperatures. Similarly, IR data confirm that down to the lowest temperatures, there is neither charge ordering nor important modification of the electronic structure. However, the temperature dependence of Raman spectra of both salts reveals a regime change at about 150 K. Additionally, using Density Functional Theory (DFT) methods, the normal vibrational modes of the neutral DMtTTF⁰ and cationic DMtTTF⁺ species and also their theoretical IR and Raman spectra were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral DMtTTF⁰ molecule. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectroscopy of CaM2+Ge2O6 (M2+ = Mg,Mn, Fe,Co, Ni,Zn) clinopyroxenes

The Raman spectra of Ge‐clinopyroxenes CaM²⁺Ge₂O₆ (M²⁺ = Mg, Mn, Fe, Co, Ni, Zn), general formula M2M1T₂O₆, are reported for the first time. Their spectral features are discussed in comparison with corresponding Si‐pyroxenes. The vibrational wavenumbers of germanates may be roughly obtained by a scale factor of about ~0.8 by those of the corresponding silicates, due to the Ge‐Si mass difference. The main peaks in the germanate Raman spectra at ~850 and ~540 cm⁻¹ may be related to Ge‐O tetrahedral stretching and chain bending, respectively; minor peaks between 200 and 400 cm⁻¹ are ascribed to bending and stretching of the non‐tetrahedral cations. Within Ge‐pyroxenes, possible correlations between crystallographic parameters and the vibrational wavenumbers are investigated. The main stretching mode at ~850 cm⁻¹ shows wavenumber changes with M²⁺ substitutions, but no simple correlation can be found with M²⁺ cation mass or size. On the other hand, the chain bending wavenumber linearly decreases with increasing ionic radius of the M²⁺ cation: the expansion of the M1 polyhedron reduces the chain kinking angle and the Ge‐Ge distances correspondingly increase. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of Ir(ppy)3 and [Ir(ppy)2 bpy]+ by infrared,Raman spectra and surface‐enhanced Raman scattering

The Raman and infrared spectra of fac ‐tris(2‐phenylpyridinato‐N,C2′)iridium(III), Ir(ppy)₃ and surface‐enhanced resonance Raman spectra of bis(2‐phenyl pyridinato‐) (2,2′bipyridine) iridium (III), [Ir(ppy)₂ (bpy)]⁺ cation were recorded in the wavenumber range 150–1700 cm⁻¹, and complete vibrational analyses of Ir(ppy)₃ and [Ir(ppy)₂ (bpy)]⁺ were performed. Most of the vibrational wavenumbers were calculated with density‐functional theory agree with experimental data. On the basis of the results of calculation and comparison of the spectra of both complexes and their analogue [Ru(bpy)₃]²⁺, we assign the vibrational wavenumbers for metal–ligand modes; metal–ligand stretching wavenumbers are 277/307 and 261/236 cm⁻¹ for Ir(ppy)₃, and 311/324, 257/270, 199/245 cm⁻¹ for [Ir(ppy)₂ bpy]⁺. Surface‐enhanced Raman scattering spectra of [Ir(ppy)₂ bpy]²⁺ were measured at two wavelengths on the red and blue edges of the low‐energy metal‐to‐ligand charge‐transfer band. According to the enhanced Raman intensities for the vibrational modes of both ligands ppy and bpy, the unresolved charge‐transfer band is deduced to consist of charge‐transfer transitions from the triplet metal to both ligands ppy and bpy. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of M3B7O13X boracites (M = Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I)

We report results of a Raman study on single crystals of 16 boracites M₃B₇O₁₃X (M = Cr,Co,Ni,Cu,Zn,Cd; X = Cl,Br,I) over a broad temperature range. The Raman modes for all boracites in their high‐temperature prototype cubic (F3c) phase are compared. With decreasing temperature, most (but not all) compounds present a transition to the low‐temperature orthorhombic phase (Pca2₁) or to a sequence of orthorhombic, monoclinic (Pa), and trigonal (R3c) phases. The variations of the Raman spectra through different phases are studied in detail. Special attention is paid to the temperature hysteresis near the transitions and the dependence of transition temperature on the direction of crystal growth for the same material. Copyright © 2014 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman scattering study of multiferroic MnWO4

We have measured polarized Raman spectra of MnWO₄ single crystals at low temperatures, and studied the temperature dependence of the various phonon modes. From our Raman studies of the MnWO₄, a new transition temperature, ∼180 K, was found. We have completely assigned the symmetries of the 18 observed Raman modes of the MnWO₄, as expected from a group theoretical analysis. These Raman modes have been classified into three groups according to weak, intermediate and strong temperature dependence of the modes in each group. Six internal modes have been identified by their weak temperature dependence of the Raman wavenumbers. The temperature dependence of the wavenumbers of the B_g modes in Mg O bonds, modes of intermediate temperature dependence group, shows an anomalous behavior under 50 K. The phonon modes of strong temperature dependence show an anomalous change at ∼180 K in the linewidths. This is believed to be a new transition temperature which involves the changes in the inter‐WO₆ octahedra structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular structure,spectroscopic (FTIR,FTIR gas phase,FT‐Raman) first‐order hyperpolarizability and HOMO–LUMO analysis of 4‐methoxy‐2‐methyl benzoic acid

Vibrational spectral analysis was carried out for 4‐methoxy‐2‐methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT‐IR) (solid, gas phase) and FT‐Raman spectroscopy in the range of 400–4000 and 10–3500 cm⁻¹ respectively. The effects of molecular association through O H···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree‐Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first‐order hyperpolarizability (β₀) of this novel molecular system and related properties (β, α₀ and Δα) of 4M2MBA are calculated using the B3LYP/cc‐pvdz basis set, based on the finite‐field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental vibrational spectra (Raman,infrared) and DFT calculations on monomeric and dimeric structures of 2‐ and 6‐bromonicotinic acid

In this work, the Fourier transform infrared and Raman spectra of 2‐bromonicotinic acid and 6‐bromonicotinic acid (abbreviated as 2‐BrNA and 6‐BrNA, C₆H₄BrNO₂) have been recorded in the region 4000–400 and 3500–50 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared intensities and Raman scattering activities, corresponding vibrational assignments and intermolecular hydrogen bonds were investigated with the help of B3LYP density functional theory (DFT) method using 6‐311++G(d,p) basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural dynamics of 4‐cyanobenzaldehyde in S2(ππ*) state

The excited state structural dynamics of 4‐cyanobenzaldehyde (p‐CNB) were studied by using the resonance Raman spectroscopy and the quantum mechanical calculations. The experimental A‐ and B‐band absorptions were, respectively, assigned to the major n_O → π₃* and π₂ → π₃* transitions according to the B3LYP‐TD/6‐31G(d) and CIS/6‐31G(d) computations, and the resonance Raman spectra. It was determined that the actual S₂(π₂π₃) state was in energy lower than S₃(π₁π₃), which was just opposite to the B3LYP‐TD/6‐31G(d) calculated order of the S₂(π₁π₃) and S₃(π₂π₃). The vibrational assignments were carried out for the A‐ and B‐band resonance Raman spectra. The B‐band resonance Raman intensities of p‐CNB were dominated by the C2–C3/C5–C6 symmetric stretch mode ν₈, the overtones nν₈ and their combination bands with the ring C–H bend mode ν₁₇, the C9–N10 stretch mode ν₆, the C7–O8 stretch mode ν₇ and the remaining modes. The conical intersection between S₁(n_Oπ₃) and S₂(π₂π₃) states of p‐CNB was determined at complete active space self‐consistent field (CASSCF)(8,7)/6‐311G(d,p) level of theory. The B‐band short‐time structural dynamics and the corresponding decay dynamics of p‐CNB were obtained by analysis of the resonance Raman intensity pattern and CASSCF computations. The resonance Raman spectra indicated that CI[S₁(n_Oπ₃)/S₂(π₁π₂π₃π₄)] located nearby the Franck–Condon region. The excited state decay dynamics evolving from the S_{2, FC}(π₂π₃) to the S₁(n_Oπ₃) state was proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

A joint FTIR,FT‐Raman and scaled quantum mechanical study of 1,3‐dibromo‐2,4,5,6‐tetra‐fluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB)

The liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Resonant Raman scattering in CdSxSe1−x nanocrystals: effects of phonon confinement,composition, and elastic strain

Optical phonon modes, confined in CdS_xSe_1−x nanocrystal (NC) quantum dots (≈2 nm in radius) grown in a glass matrix by the melting‐nucleation method, were studied by resonant Raman scattering (RRS) spectroscopy and theoretical modeling. The formation of nanocrystalline quantum dots (QDs) is evidenced by the observation of absorption peaks and theoretically expected resonance bands in the RRS excitation spectra. This system, a ternary alloy, offers the possibility to investigate the interplay between the effects of phonon localization by disorder and phonon confinement by the NC/matrix interface. Based on the concept of propagating optical phonons, which is accepted for two‐mode pseudo‐binary alloys in their bulk form, we extended the continuous lattice dynamics model, which has successfully been used for nearly spherical NCs of binary materials, to the present case. After determining the alloy composition for NCs (that was evaluated with only 2–3% uncertainty using the bulk longitudinal optical phonon wavenumbers) and the NC size (using atomic force microscopy and optical absorption data), the experimental RRS spectra were described rather well by this theory, including the line shape and polarization dependence of the scattering intensity. Even though the presence of a compressive strain in the NCs (introduced by the matrix) masks the expected downward shift owing to the phonons' spatial quantization, the asymmetric broadening of both Raman peaks is similar to that characteristic of NCs of pure binary materials. Although with some caution, we suggest that both CdSe‐like and CdS‐like optical phonon modes indeed are propagating within the NC size unless the alloy is considerably heterogeneous. Copyright © 2011 John Wiley & Sons, Ltd.     

The electronic delocalization in para‐substituted β‐nitrostyrenes probed by resonance Raman spectroscopy and quantum‐chemical calculations

The electronic (UV‐vis) and resonance Raman (RR) spectra of a series of para‐substituted trans‐β‐nitrostyrenes were investigated to determine the influence of the electron donating properties of the substituent (X = H, NO₂, COOH, Cl, OCH₃, OH, N(CH₃)₂, and O⁻) on the extent of the charge transfer to the electron‐withdrawing NO₂ group directly linked to the ethylenic (C = C) unit. The Raman spectra and quantum chemical calculations show clearly the correlation of the electron donating power of the X group with the wavenumbers of the ν_s(NO₂) and ν (C = C)_sty normal modes. In conditions of resonance with the lowest excited electronic state, one observes for X = OH and N(CH₃)₂ that the symmetric stretching of the NO₂, ν_s(NO₂), is the most substantially enhanced mode, whereas for X = O⁻, the chromophore is extended over the whole molecule, with substantial enhancement of several carbon backbone modes. Copyright © 2008 John Wiley & Sons, Ltd.     

The temperature dependence of the Raman spectra of chromium‐doped titanite (CaTiOSiO4)

The temperature dependence of the Raman bands of Cr⁴⁺ modes which show enhanced intensities due to pre‐resonance effects is reported from 293 to 673 K in chromium‐doped titanite (CaTiOSiO₄). Some aspects of the temperature dependence of Raman bands in pure, synthetic titanite which have not been previously published are also included in this study. Two Raman‐active components of A_g and B_g symmetry, respectively, of the symmetric Si–O mode in titanite are predicted under P2₁/a symmetry and also been identified in this phase for the first time. The one component of B_g symmetry disappears just above the antiferroelectric–paraelectric transition at ~500 K in accordance with the predictions under A2/a symmetry for the high‐temperature phase. Two resonance‐enhanced components of the Cr⁴⁺–O stretch are also evident in the P2₁/a phase and only one could be identified in the A2/a phase, again in accordance with group‐theoretical predictions. These observations can be used to characterize the P2₁/a and A2/a phases of pure synthetic and chromium‐doped titanite. The temperature dependence of the Cr⁴⁺–O modes can be approximated by two‐dimensional Ising behavior with the critical exponent β ≈ 1/8 below 450 K. Between 450 and 498 K, anomalous behavior is observed and this could be due to the appearance of mobile anti‐phase boundaries (APBs). Anomalous behavior also persists to temperatures above 500 K. The half‐width of the Ti–O stretching mode reflects the influence of the order parameter (Ti–O displacements) as well as mobile anti‐phase boundaries. No evidence could be found of the existence of other ions such as Cr⁴⁺‐ions in Ti‐sites and/or Cr³⁺‐ions also in Ti‐positions in Cr‐doped titanite in the Raman spectra using different laser lines to excite the spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of SERRS and RRS excitation profiles of [Fe(tpy)2]2+ (tpy = 2,2':6',2'‐terpyridine) supported by DFT calculations: effect of the electrostatic bonding to chloride‐modified Ag nanoparticles on its vibrational and electronic structure

Nonresonance (or normal) Raman scattering (NRS), resonance Raman scattering (RRS), surface‐enhanced Raman scattering (SERS), and surface‐enhanced RRS (SERRS) spectra of [Fe(tpy)₂]²⁺ complex dication (tpy = 2,2':6',2''‐terpyridine) are reported. The comparison of RRS/NRS and SERRS/SERS excitation profiles of [Fe(tpy)₂]²⁺ spectral bands in the range of 445–780 nm is supported by density functional theory (DFT) calculations, Raman depolarization measurements, comparison of the solid [Fe(tpy)₂](SO₄)₂ and solution RRS spectra, and characterization of the Ag nanoparticle (NP) hydrosol/[Fe(tpy)₂]²⁺ SERS/SERRS active system by surface plasmon extinction spectrum and transmission electron microscopy image of the fractal aggregates (D = 1.82). By DFT calculations, both the Raman active modes and the electronic states of the complex have been assigned to the symmetry species of the D_2d point group. It has been demonstrated that upon the electrostatic bonding of the complex dication to the chloride‐modified Ag NPs, the geometric and ground state electronic structure of the complex and the identity of the three different metal‐to‐ligand charge transfer (¹MLCT) electronic transitions remain preserved. On the other hand, the effect of ion pairing manifests itself by a slight change in localization of one of the electronic transitions (with max. at 552 nm) as well as by promotion of the Herzberg–Teller activation of E modes resulting from coupling of E and B₂ excited electronic states. Finally, the very low, 1 × 10⁻¹¹ M SERRS spectral detection limit of [Fe(tpy)₂]²⁺ at 532‐nm excitation is attributed to a concerted action of the electromagnetic and molecular resonance mechanism, in conjunction to the electrostatic bonding of the complex dication to the chloride‐modified Ag NP surface. Copyright © 2014 John Wiley & Sons, Ltd.     

Study of asymmetric wavenumber shift of the Fermi doublet ν1 − 2ν2 in the Raman spectrum of liquid carbon disulfide

The Raman spectra of liquid carbon disulfide (CS₂) diluted with benzene (C₆H₆) have been measured. By changing the CS₂, the concentration, we found an asymmetric wavenumber shift phenomenon. With decreasing concentration of CS₂, the position of the ν₁ (655 cm⁻¹) band remains practically unchanged, and the 2ν₂ (796 cm⁻¹) band shifts toward higher wavenumbers. To interpret this asymmetric wavenumber shift phenomenon of the Fermi doublet ν₁ − 2ν₂ in the Raman spectra satisfactorily, we propose a modified Bertran model. The values of the Fermi resonance (FR) parameters of CS₂ at different concentrations were calculated using the Bertran equations. In addition, we found the fundamental ν₂, which should be independent of the FR interaction, shifted to higher wavenumbers as the concentration decreased. This shift was probably driven by the tuning of the FR. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvent‐dependent structural dynamics of 2(1H)‐pyridinone in light absorbing S4(ππ*) state

The B‐band resonance Raman spectra of 2(1H)‐pyridinone (NHP) in water and acetonitrile were obtained, and their intensity patterns were found to be significantly different. To explore the underlying excited state tautomeric reaction mechanisms of NHP in water and acetonitrile, the vibrational analysis was carried out for NHP, 2(1D)‐pyridinone (NDP), NHP–(H₂O)_n (n = 1, 2) clusters, and NDP–(D₂O)_n (n = 1, 2) clusters on the basis of the FT‐Raman experiments, the B3LYP/6‐311++G(d,p) computations using PCM solvent model, and the normal mode analysis. Good agreements between experimental and theoretically predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands in both the FT‐Raman and the resonance Raman spectra. The results indicated that most of the B‐band resonance Raman spectra in H₂O was assignable to the fundamental, overtones, and combination bands of about ten vibration modes of ring‐type NHP–(H₂O)₂ cluster, while most of the B‐band resonance Raman spectra in CH₃CN was assigned to the fundamental, overtones, and combination bands of about eight vibration modes of linear‐type NHP–CH₃CN. The solvent effect of the excited state enol‐keto tautomeric reaction mechanisms was explored on the basis of the significant difference in the short‐time structural dynamics of NHP in H₂O and CH₃CN. The inter‐molecular and intra‐molecular ESPT reaction mechanisms were proposed respectively to explain the Franck–Condon region structural dynamics of NHP in H₂O and CH₃CN.Copyright © 2015 John Wiley & Sons, Ltd.     

First‐order Raman scattering of the MAX phases Ta4AlC3, Nb4AlC3, Ti4AlN3, and Ta2AlC

Herein, we report on the Raman spectra of the following ternary hexagonal carbides and nitrides (MAX phases): Ta₄AlC₃, Ta₂AlC and Ti₄AlN₃. We also present the Raman‐active modes of α‐ and β‐Ta₄AlC₃, Nb₄AlC₃ and Ti₄AlN₃, – also referred to as the 413 MAX phases – as predicted from first principles calculations using density functional theory. We compare the obtained experimental and calculated results with previous studies on Ta₂AlC and Ti₄AlN₃. The vibrational behavior associated with the Raman‐active modes for the 413 phases has been identified for the first time. In general, the agreement is good between theory and experiment. The experimental and calculated results indicate that the modes at low wavenumbers ‐ dominated by the Al atoms ‐ are a weak function of chemistry and the differences in energy can be traced to variations in the reduced mass. The modes at higher wavenumbers are dominated by the C and N atoms and show a strong dependence on the unit cell chemistry, with the Ta–C bond being stiffer than the Nb–C bond, which is in turn stiffer than Ti–N. Copyright © 2011 John Wiley & Sons, Ltd.     

Density functional theory calculation and vibrational spectral analysis of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one

The Fourier transform infrared (4000–400 cm⁻¹) and Fourier transform Raman (3500–500 cm⁻¹) spectra of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one (Warfarin) have been measured and calculated. The structure optimization has been made using density functional theory (DFT) calculations. Complete vibrational assignments of the observed spectra have been compared with theoretical wavenumbers. The wavenumber increasing in the methyl group shows the electronic hyperconjugation effect. The natural bond orbital (NBO) analysis reveals the hyperconjugation interaction and the intramolecular hydrogen bonding. The first‐order hyperpolarizability has been calculated. Copyright © 2009 John Wiley & Sons, Ltd.     

MREI‐model calculations of Raman‐active modes in layered mixed crystals TiS2−xSex(0≤x≤2)

A modified random‐element isodisplacement model has been developed and used to calculate the concentration dependence of the wavenumbers of Raman‐active modes in mixed crystal system, TiS_2−xSe_x(0≤x≤2). Earlier theoretical work, based on the Jaswal model, predicted a phase transition in this system on cooling up to 125 K temperature for the composition x ≥ 1.2. But recently reported resistivity measurements did not find the existence of any phase transition for a composition x < 1.4 on cooling. Our calculations show these findings and give remarkably better fitting to Raman data. The estimated values of the force constants are found to lie generally in the range 10⁵–10⁶ amu cm⁻². Copyright © 2007 John Wiley & Sons, Ltd.