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.     

Resonance Raman and electronic absorption study of free‐base tetraphenylporphine diacid dispersed in polymethylcyanoacrylate

We report a resonance Raman study on free‐base tetraphenylporphine (H₂TPP) and its chemically prepared diacid dispersed in polymethylcyanoacrylate (PMCA). Photoexcitation of the neutral porphine by laser light leads irreversibly to the formation of the diacid, with the π‐cation radical as intermediate species. Resonance Raman (RR) spectra of the diacid dispersed in the polymer obtained with 441.6 nm in the wavenumber region of 100–1650 cm⁻¹ are recorded. Wavenumbers with other excitation lines are also reported for the diacid species. Some bands assigned to out‐of‐plane vibrational modes and forbidden under ideal D_2h symmetry are also observed in the resonance Raman spectra of the diacid. These bands arise from the out‐of‐plane distortions, which reduce the symmetry of the molecule. These findings are supported by the electronic absorption studies of the diacid in the polymer. Copyright © 2007 John Wiley & Sons, Ltd.     

Overtone and combination features of G and D peaks in resonance Raman spectroscopy of the C78H26 polycyclic aromatic hydrocarbon

We have studied the Raman spectra of C₇₈H₂₆, a polycyclic aromatic hydrocarbon with D_2h symmetry point group resembling a longitudinally confined graphene ribbon (or a graphene island) with armchair edge. The experimental spectra recorded with several excitation laser lines have been compared with the results from a theoretical analysis of the resonant Raman response based on density functional theory calculations. Compared to previous investigation the spectra show better signal‐to‐noise ratio, which allows determining previously unresolved weak spectroscopic features. We have extended our analysis to the overtone and combination region (i.e. above 2000 cm⁻¹) demonstrating the presence of signals attributable to 2G, G + D, 2D, D_j + D_k and G + acoustic‐like modes. Moreover, we have measured the temperature dependence of the G peak position, which turns out to show a similar behavior with respect to that of graphene/graphite. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Raman investigation of sol–gel‐derived relaxor ferroelectric thin films

Pb(Fe_2/3W_1/3)O₃ (PFW) thin films were deposited on platinized silicon substrate by a chemical solution deposition technique. Room‐temperature X‐ray diffraction (XRD) revealed a pure cubic crystal structure of the investigated material. The microstructure indicated good homogeneity and density of the thin films. A Raman spectroscopic study was carried out on PFW to study the polar nano‐regions in the temperature range 85–300 K. The Raman spectra showed a change in the peak intensity and a shift towards the lower wavenumber side with temperature. The Raman spectra also revealed the transition from the relaxor to the paraelectric state of PFW. There was no evidence of a soft mode in the low‐temperature region, in contrast to the normal ferroelectric behavior. The polar nano‐regions tend to grow and join at low temperatures (∼85 K), which become smaller with increase in temperature. The presence of strong Raman spectra in the cubic phase of the material is due to the presence of distributed Fm3m(Z = 2) symmetry nano‐ordered regions in the Pm3m(Z = 1) cubic phase. Copyright © 2007 John Wiley & Sons, Ltd.     

Involvement of weak C?H···X hydrogen bonds in metal‐to‐semiconductor regime change in one‐dimensional organic conductors (o‐DMTTF)2X (X = Cl,Br, and I): combined IR and Raman studies

We report on the infrared (IR) and Raman studies of the three isostructural quasi‐one‐dimensional cation radical salts of 3,4‐dimethyl‐tetrathiafulvalene (o‐DMTTF)₂X (X = Cl, Br, and I), which all exhibit metallic properties at room temperature and undergo transitions to a semiconducting state in two steps: a soft metal‐to‐semiconductor regime change in the temperature region T_ρ = 5–200 K and then a sharp phase transition at about T_MI = 50 K. Polarized IR reflectance spectra (700–16 000 cm⁻¹) and Raman spectra (50–3500 cm⁻¹, excitation λ = 632.8 nm) of single crystals were measured as a function of temperature (T = 5–300 K) to assess the eventual formation of a charge‐ordered state below 50 K. Additionally, the temperature dependence of the IR absorption spectra of powdered crystals in KBr discs was also studied. The Raman spectra and especially the bands related to the CC stretching vibration of o‐DMTTF provide unambiguous evidence of uniform charge distribution on o‐DMTTF down to the lowest temperatures, without any modification below 50 K. However, the temperature dependence of Raman spectra indicates a regime change below about 200 K. Temperature dependence of both electronic dispersion and vibrational features observed in the IR spectra also clearly confirms the regime change below about 200 K and shows the involvement of C H···X hydrogen bonds in the electronic localization; some spectral changes can be also related with the phase transition at 50 K. Additionally, using density functional theory methods, the normal vibrational modes of the neutral o‐DMTTF⁰ and cationic o‐DMTTF⁺ species, as well as their theoretical IR and Raman spectra, were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral o‐DMTTF molecule. Copyright © 2011 John Wiley & Sons, Ltd.     

On the relative intensities of the Raman active fundamentals,r0 structural parameters,and pathway of chair–boat interconversion of cyclohexane and cyclohexane‐d12

Raman spectra of liquid cyclohexane, C₆H₁₂, and deuterated cyclohexane, C₆D₁₂, were recorded with both parallel and perpendicular polarizations. The observed vibrational wavenumbers, depolarization ratios, and their intensities were measured and compared with the corresponding predicted values as well as the experimental values previously reported. The conformational energetics were obtained with the Møller–Plesset perturbation method to the second order [MP2(full)] as well as with density functional theory by the B3LYP method utilizing a variety of basis sets. The average ab initio predicted difference in energy between the more stable chair form (D_3d) and the less stable twisted‐boat form (D₂) is 2213 cm⁻¹ (26.47 kJ/mol), with a similar value of 2223 cm⁻¹ (26.59 kJ/mol) from the density function theory calculations. By using two dihedral angles as variables, we calculated the chair–boat interconversion pathway for cyclohexane at the MP2(full)/6‐31G(d) level. The harmonic force constants, Raman intensities, depolarization values, and the potential energy distribution were predicted from both MP2(full) and B3LYP calculations with the 6‐31G(d) basis set and compared with the experimental values for the chair form when available. The ‘adjusted’ r₀ structural parameters were obtained from MP2/6‐311 + G(d,p) calculations and previously reported microwave rotational constants of five isotopomers of cyclohexane: i.e. 1,1‐d₂, ¹³C‐1,1‐d₂, 1,1,2,2,3,3‐d₆, and d₁ (equatorial and axial). The determined distances in Å are: r(CC) = 1.536(3), r(CH)_ax = 1.098(1); r(CH)_eq = 1.095(1); and the angles in degrees: ∠CCH_ax = 108.8(3); ∠CCH_eq = 110.2(3); ∠CCC = 111.1(3); and ∠HCH = 107.6(3) with dihedral angle ∠CCCC = 55.7(3). These values are compared with those previously reported and it is found that the difference in the r₀ distances (0.003 Å) between the two CH values is much smaller than the difference (0.008 Å) previously reported for the r_s values. Copyright © 2008 John Wiley & Sons, Ltd.     

Theoretical elucidation of the origin of surface‐enhanced Raman spectra of PCB52 adsorbed on silver substrates

To better understand experimentally observed surface‐enhanced Raman Scattering (SERS) of polychlorinated biphenyls (PCBs) adsorbed on nanoscaled silver substrates, a systematic theoretical study was performed by carrying out density functional theory and time‐dependent density functional theory calculations. 2,2′,5,5′‐tetrachlorobiphenyl (PCB52) was chosen as a model molecule of PCBs, and Ag_n (n = 2, 4, 6, and 10) clusters were used to mimic active sites of substrates. Calculated normal Raman spectra of PCB52–Ag_n (n = 2, 4, 6, and 10) complexes are analogical in profile to that of isolated PCB52 with only slightly enhanced intensity. In contrast, the corresponding SERS spectra calculated at adopted incident light are strongly enhanced, and the calculated enhancement factors are 10⁴ ~ 10⁵. Thus, the experimentally observed SERS phenomenon of PCBs supported on Ag substrates should correspond to the SERS spectra rather than the normal Raman spectra. The dominant enhancement in Raman intensities origins from the charge transfer resonance enhancement between the molecule and clusters. Copyright © 2014 John Wiley & Sons, Ltd.     

Vibrational Analysis of Coherent Anti-Stokes Resonance Raman Spectra from Bacteriorhodopsin Containing Isotopically Substituted Retinal Chromophores

Vibrational spectra recorded by coherent anti-Stokes resonance Raman scattering (CARS) from bacteriorhodopsin (BR) samples containing isotopically substituted (²H and ¹³C) retinal chromophores were measured using high repetition rate, low-power, picosecond pulsed excitation (λ₁=580 nm and λ_s=640±3 nm). These picosecond resonance CARS (PR/CARS) data were analyzed via third-order susceptibility relationships [χ ^{( 3 )} ] to obtain band origins, bandwidths, relative intensities, and electronic phase factors assignable to all significant vibrational Raman features in the 1490–1700 cm⁻¹ wavenumber region (the ethylenic stretching and C = N–H rocking or Schiff base modes). Isotopic substitution selectively places ²H at C₁₅, ¹³C singly at the C₁₀ position and at the C₁₄ position, and ¹³C simultaneously in positions of C₁₄ and C₁₅. Each isotopic BR sample was examined not only in H₂O, but also in D₂O, which places a ²H at the Schiff base nitrogen of the retinal. In addition, PR/CARS data were recorded from each isotopic BR sample following either light adaptation [i.e. the BR sample contained a single retinal isomer (all- trans , 15- anti or BR-570)] or dark adaptation [i.e. the BR sample contained a mixture of comparable amounts of retinal isomers (BR-570 and 13- cis , 15- syn or BR-548)]. Excellent agreement was found between the vibrational features observed by PR/CARS and those obtained from spontaneous resonance Raman measurements from the same isotopically substituted BR pigments. Several new vibrational features were also found from the PR/CARS data. Vibrational Raman data from three of the isotopic BR samples in D₂O are reported for the first time.     

Density functional theory calculations and vibrational spectra of p‐bromonitrobenzene

FT‐IR and FT‐Raman spectra of p‐bromonitrobenzene (p‐BNB) have been recorded in the region 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The molecular structure, geometry optimization, vibrational wavenumbers have been investigated. The spectra were interpreted with the aid of normal coordinate analysis based on the density functional theory (DFT) using the standard B3LYP/6‐31G method and basis set combination and was scaled using multiple scale factors yielding good agreement between observed and calculated wavenumbers. The results of the calculations are applied to simulate infrared and Raman spectra of the title compound which showed reasonable agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

First and second‐order Raman scattering of B6O

First and second‐order Raman spectra of B₆O and their dependence on the wavelength of the excitation line from IR (infrared) to deep UV (ultraviolet) has been studied. The first‐order Raman spectra contain 11 well‐resolved lines of the 12 expected modes 5 A_1g + 7 E_g (space group R‐3m, point group D_3d). The second‐order Raman spectra contains eight lines that are resolved only in the case of the 244‐nm excitation line. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

The interaction of K⁺ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm⁻¹. The wavenumber position of the band at ~529 cm⁻¹ shows a red shift of 14 cm⁻¹, while the Raman band at ~634 cm⁻¹ shows a blue shift of 10 cm⁻¹ with the increasing x from 1 to 5 M. The intensity ratio I₆₃₄/I₅₂₉ is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K⁺] complex in the solution. The new Raman band appeared at ~1079 cm⁻¹ in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K⁺ with ZAla, the structures of ZAla and the [ZAla + K⁺] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO⁻, and therefore, COO⁻ would be the most probable site for the interaction of K⁺ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K⁺] and the [ZAla⁻ + K⁺] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm⁻¹ may be used as the Raman fingerprint for the interaction of K⁺ with COO⁻ of the ZAla and ZAla⁻. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman spectral studies of Zr4+‐rich BaZrxTi1−xO3(0.5⩽x⩽1.00) phase diagram

This paper reports a systematic study of the composition and the temperature‐dependent‐Raman spectra of Zr⁴⁺‐rich BaZr_xTi_1−xO₃ (BZT) ceramic compositions (0.50⩽x⩽1.00). On the basis of the dielectric behavior of Zr rich BZT ceramics, the observed relaxor behavior has been hypothesized as a result of increasing long‐range interactions of nanosized, Ti⁴⁺‐rich polar regions in a Zr⁴⁺‐rich nonpolar matrix. Beyond an optimum concentration of BaTiO₃ (BT) in the nonpolar matrix of BaZrO₃ (x⩽0.75), a critical size and density of the polar regions is reached when the polar clusters start showing the relaxor like behavior, which finally show classical relaxor behavior for compositions with x = 0.5 and 0.6. This hypothesis is strongly supported from the Raman data on Zr‐rich BZT presented in this paper. Well‐defined BT Raman spectra for 5% BT in BZT composition were recorded, which followed completely up to the 50% Ti addition in the BZT samples. The temperature‐dependent Raman spectra collected on the BZT ceramics far beyond the dielectric transition temperatures supported the existence of the nano‐polar BT regions, like in typical relaxor samples. The full width at half‐maximum (FWHM), integrated intensity of the peaks in the Raman spectra has been analyzed to further support the conclusions. Copyright © 2008 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of line positions and assignments for the ν2 and ν3 bands of 13C2H4

High‐resolution stimulated Raman spectra of¹³C₂H₄ in the regions of the ν₂ and ν₃ Raman active modes have been recorded at two temperatures (145 and 296 K) based on the quasi continuous‐wave (cw) stimulated Raman spectrometer at Instituto de Estructura de la Materia IEM‐CSIC in Madrid. A tensorial formalism adapted to X₂Y₄ planar asymmetric tops with D_2h symmetry (developed in Dijon) and a program suite called D_2hTDS (now part of the XTDS/SPVIEW spectroscopic software) were proposed to analyze and calculate the high‐resolution spectra. A total of 103 and 51 lines corresponding to ν₂ and ν₃ Raman active modes have been assigned and fitted in wavenumber with a global root mean square deviation of 0.54 × 10⁻³ and 0.36 × 10⁻³ cm⁻¹, respectively. Due to the fact that the Raman scattering effect is weak, we did not perform in this contribution the line intensities analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantitative analysis of the phonon confinement effect in arbitrarily shaped Si nanocrystals decorated on Si nanowires and its correlation with the photoluminescence spectrum

Arrays of single‐crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) are grown by a metal‐assisted chemical etching process using silver (Ag) as the noble metal catalyst. The metal‐assisted chemical etching‐grown Si NWs exhibit strong photoluminescence (PL) emission in the visible and near infrared region at room temperature. Quantum confinement of carriers in the Si NCs is believed to be primarily responsible for the observed PL emission. Raman spectra of the Si NCs decorated on Si NWs exhibit a red shift and an asymmetric broadening of first‐order Raman peak as well as the other multi‐phonon modes when compared with that of the bulk Si. Quantitative analysis of confinement of phonons in the Si NCs is shown to account for the measured Raman peak shift and asymmetric broadening. To eliminate the laser heating effect on the phonon modes of the Si NWs/NCs, the Raman measurement was performed at extremely low laser power. Both the PL and Raman spectral analysis show a log‐normal distribution for the Si NCs, and our transmission electron microscopy results are fully consistent with the results of PL and Raman analyses. We calculate the size distribution of these Si NCs in terms of mean diameter (D₀) and skewness (σ) by correlating the PL spectra and Raman spectra of the as‐grown Si NCs decorated on Si NWs. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman identification of lonsdaleite in Popigai impactites

Micro‐Raman spectroscopy and X‐ray diffraction method (XRD) were used to characterize impact carbonaceous rocks excavated from the Popigai crater (Siberia). The deconvolution of the first‐order Raman spectra of the rocks containing different amounts of carbon phases (diamond, lonsdaleite and graphite) allowed the identification of lonsdaleite spectrum. The most intensive band at 1292–1303 cm⁻¹ was ascribed to A_1g vibration mode of lonsdaleite, whereas the less intense band at 1219–1244 cm⁻¹ was attributed, in agreement with previously reported ab initio calculations, to E_2g vibration mode. The established correlation between the intensities of Raman and XRD peaks permits a rough estimation of lonsdaleite/diamond phase ratio in the impact rocks using micro‐Raman measurements. The second‐order Raman spectra of lonsdaleite–diamond rocks were recorded. Copyright © 2014 John Wiley & Sons, Ltd.     

Multipeak fitting analysis of Raman spectra on DLCH film

The hydrogenated diamond‐like carbon (DLCH) film with 1‐µm thickness is deposited by direct hydrocarbon gas ion beam method on silicon wafer and annealed at 400 °C. Detailed Raman spectra feature are fitted from nine sets of different peak fitting functions, including Gaussian, Lorentzian and Breit‐Wigner‐Fano (BWF) functions. These fitting results obtained from a two‐peak combination show some specific variances on the G peak position, FWHM_G and I_D/I_G ratio for as‐deposited and as‐annealed DLCH films. The most popular two‐peak fitting method with full Gaussian function tends to exhibit a higher ratio of the G peak position shift and higher I_D/I_G ratio than others fitting methods, the drastic difference among the most popular G (G) & G (D) and B (G) & L (D) schemes also have brought out in I_D/I_G ratio. However, for a more complex four‐peak Gaussian function fitting Raman spectra, the I_D/I_G ratio is close to that of a two‐peak fitting function with a mixture functions of BWF (G) and L (D). Furthermore, a series of systematic peak fitting procedures and comparisons of Raman spectra have been discussed in this study. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural Characterization of RF‐Sputtered a‐C:N Thin Films by Raman,IR, and X‐ray Reflectometry Spectroscopies

Abstract

Amorphous carbon nitride thin films (a‐C:N) were deposited from a carbon target, at room temperature onto silicon substrates, by reactive RF sputtering in a gas mixture of argon and nitrogen. The structural properties of these films have been studied by Raman, infrared (IR), and X‐ray reflectometry spectroscopies. Both the IR and Raman spectra of the a‐C:N films reveal the presence of C–C, C?C, C?N, and C≡N bonding types. The Raman spectra analysis shows, an increase of the C≡N triple bonds content when the concentration of nitrogen C(N₂) in the gas mixture is increased. The Raman intensities ratio between the disorder (D) and graphitic (G) bands increases with C(N₂) suggesting an increased disorder with the incorporation of nitrogen in the carbon matrix. The effect of C(N₂) on the density of a‐C:N films was also investigated by X‐ray reflectometry measurement. The increase of the nitrogen concentration C(N₂) was found to have a significant effect on the density of the films: as C(N₂) increases from 0 to 100%, the density of the a‐C:N films decreases slightly from 1.81 to 1.62 g/cm³. The low values of density of the a‐C:N films were related (i) to the absence of C–N single bonds, (ii) to the increase of disorder introduced by the incorporation of nitrogen in the carbon matrix, and (iii) to the presence of the bands around 2350 cm^?1 and 3400 cm^?1 associated with the C–O bond stretching modes and the O–H vibration, respectively, suggesting a high atmospheric contamination by oxygen and water. The presence of these bands suggests the porous character of the studied samples.     

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.     

Correlations between Raman parameters and elemental composition in lead and lead alkali silicate glasses

This article examines the influence of the composition on the Raman spectra of lead silicate glass. Modern and historic lead alkali glasses and high‐lead glazed ceramics were analysed complementarily by Raman spectrometry and elemental techniques, either electron microprobe, proton induced X‐ray emission (PIXE) or scanning electron microscope with energy dispersive spectrometry (SEM‐EDS). The results showed that lead alkali silicate and high‐lead silicate glasses can be easily distinguished from their Raman spectra profile. In lead alkali silicate glasses, continuous variations were observed in the spectra with the compositional change. In particular, the position of the intense peak around 1070 cm⁻¹ was linearly correlated to the lead content in the glass. A unique decomposition model was developed for the spectra of lead alkali silicate glasses. From the combination of the Raman and elemental analyses, correlations were established between the spectral components and the composition. These correlations permitted to interpret the spectra and access additional compositional information, such as the lead content from area ratio A₉₉₀/A_900–1150, the total alkali + alkaline‐earth content from the area ratio A₁₁₀₀/A_900–1150 or the silica content from the area ratio A₁₁₅₀/A_900–1150. In lead silicate glass containing over 25 mol% PbO, the compositional variation induced no variation in the SiO₄ network region of the Raman spectra [150–1350 cm⁻¹], therefore no correlations and compositional information could be gained from the glass spectra in this range of composition. This new development of Raman spectroscopy for the analyses of glass will be very valuable for museums to not only access compositional information non‐destructively but also to understand the structural changes involved with their alteration. Copyright © 2008 John Wiley & Sons, Ltd.