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Infrared (IR) and Raman spectroscopy have been used to examine the vibrational characteristics of a series of three macrocyclic tetraynes in comparison with an acyclic analog. By changing the length of the alkyl tether of the macrocycles, varying degrees of bending of the tetrayne moiety can be achieved, and the joint use of IR and Raman spectroscopies provides an avenue to probe the impact of bending on the sp-chain. The spectroscopic data show a general trend toward decreasing activation of Raman bands in the IR spectra, and vice versa, as bending of the polyyne chain is decreased. Density functional theory calculations provide a detailed rationalization of the experimental observations. Copyright © 2011 John Wiley & Sons, Ltd.

Functionalized perfluoropolyethers are investigated by infrared spectroscopy with the aim to give a quantitative estimate of the carboxylic acid groups species; since hydrogen bonded moieties have been observed, also the relative distribution of the associated species has been determined. The study is based both on measured and on theoretically predicted infrared intensities, as obtained by density functional theory (DFT) calculations on model systems.

Amorphous fluorinated optical polymers, characterized by high transparency in the visible and near infrared spectra, high glass transition temperature and very good resistance to chemical environment, have been developed by co-polymerisation of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD). In this work we study at molecular level the effect of the introduction of the bulky TTD unit in a perfluoroalkyl chain. In particular the effect on the molecular structure and chain flexibility is investigated and spectroscopic markers correlated to chemical and structural defects are identified. The study includes a thorough experimental spectroscopic analysis (infrared and Raman spectra) of several different copolymer samples and a modelling based on Density Functional Theory calculations and semiempirical calculations on suitable model molecules.

We have analyzed a set of 51 PAHs whose structures have been hypothesized from mass spectrometry data collected on samples extracted from carbon particles of combustion origin. We have obtained relationships between infrared absorption signals in the fingerprint region (mid-IR) and the chemical structures of PAHs, thus proving the potential of IR spectroscopy for the characterization of the molecular structure of aromatic combustion products. The results obtained here for the spectroscopic characterization of PAHs can be also of interest in Materials Science and Astrophysics.

Calcium oxalate is found in nature in three different crystalline states determined by the number of H2O in the unit formula (whewellite CaC2O4·H2O, COM; weddellite CaC2O4·(2 + x)H2O, COD and caoxite CaC2O4·3H2O, COT). The properties of these materials are relevant in the field of biomedicine, cultural heritage and mineralogy. In two previous papers, we have used X-ray diffraction and vibrational spectroscopy (infrared and Raman) to derive information on crystal and molecular structures of COM and COD. In this paper, we complete the synthesis and analysis on the third form, COT, and present a comparative study of the data collected from the three crystalline states. The experiments clearly highlight the role played by the H2O molecules linked within the structure by different kinds of hydrogen bonds. The vibrational assignment of the infrared and Raman bands are critically proposed. The fact relevant for the work in biomedicine, cultural heritage and crystallography is that a simple examination of the spectra allows quickly to determine the chemical nature of the material in an unknown sample even in a minute quantity or in awkward experimental conditions.

Diarylethenes bearing electro-donating and electro-withdrawing substituents in the 5,5‘-positions of the thiophene unit were studied theoretically (DFT, B3LYP) to understand the effect of the substituents on the infrared spectrum in the two stable forms. The photochromic molecule with the electro-donating substituent showed the largest difference in the infrared (IR) spectrum due to the push−pull−push structure. It was chosen to build a memory film with a readout process in the mid-IR. Information written on the photochromic film was read using a setup based on an infrared camera (multibolometer) and a filtered broadband Globar source. The results showed that the readout process worked without matching any specific absorption band. A good contrast was obtained also with a single camera frame (45 ms).

A theoretical investigation is presented aimed to the interpretation of the spectroscopic behaviour of the methoxy group in molecules belonging to the class of hydrofluoroethers. The simulation of infrared and Raman spectra of four different stable conformers of CH 3 –O–CF 2 –CF 2 –O–CH 3 and the comparison with the experimental spectra allow to propose a vibrational band assignment in the CH stretching region. This clarifies the role of the CF 2 group in determining the electronic properties and spectroscopic parameters of methyl CH bonds when back-donation of electronic charge take place from oxygen.

The vibrational Infrared and Raman Spectra of a MgCl 2 -TiCl 4 Ziegler-Natta catalyst precursor with a 50/1 MgCl 2 /TiCl 4 ratio have been recorded. The Raman spectrum of this catalyst precursor, in the range 50-500 cm -1 , shows clear scattering lines which can be assigned to the complex MgCl 2 -TiCl 4 , well separated from those of the initial species. Analogous, but less clear signals can be found in the infrared spectrum. Vibrational symmetry analysis and quantum chemical calculations of suitable models of MgCl 2 -TiCl 4 complex have been made for the interpretation of the experimentally recorded spectra. The observed spectroscopic signals can be explained in terms of the existence of only one type of MgCl 2 -TiCl 4 complex where the TiCl 4 molecules are complexed on the MgCl 2 along the (110) lateral cuts in a local C 2v symmetry with the Ti atoms in an octahedral coordination.

In this article we focus on the conformational dependence of molecular hyperpolarizabilities and on the related infrared and Raman intensities for molecules where π electron delocalization and/or back-donation by oxygen lone pairs can occur. Ab initio calculations at the Hartree–Fock level have been performed on anisole and 4-nitro-anisole with 3-21G and 6-31G∗∗ basis sets. Vibrational properties and second and third order molecular polarizabilities have been studied as a function of the torsional angle describing the rotation of the O–(CH3) group about the φ-O bond. In these systems two competing effects can take place, namely back-donation and conjugation. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group. These results are used in the interpretation of the infrared spectrum of many compounds which show a characteristic strong and low frequency infrared CH stretching vibration, previously assigned to a back-donation effect. However, conjugation dependent optical properties, such as the vibrational pattern, the intensity of the collective modes, the first (β) and second order (γ) hyperpolarizabilities are almost constant with respect to changes of the torsional angle.

Molecular properties of oligo-para-phenylenes are determined mostly by the combined effect of π electron delocalization and intra-ring confinement. In order to study their relative role, we have carried out an ab initio study on biphenyl and terphenyl. Energies of formation, geometrical parameters, vibrational spectra and molecular hyperpolarizabilities are studied (using the 3-21G basis) as function of the torsional angle between two adjacent rings and the number of rings in the molecule. Relaxation contribution to first- and second-order hyperpolarizabilities (βr and γr, respectively) are obtained with a vibrational method from computed frequencies, infrared and Raman intensities. Raman lines of Я-containing normal modes progressively weaken when the systems are distorted. Similarly the component of γr along the chain axis (γzzzzr) and the orientation average 〈γr〉 decrease. For planar molecules, Raman intensities and molecular hyperpolarizabilities show a superlinear dependence upon the number of rings in the chain, while when adjacent rings lie on perpendicular planes an almost linear dependence is obtained. The optical properties of the para-phenylenes studied can be predicted by the simple addition of the corresponding values for the repeating unit (benzene) only in the conformationally distorted case. This fact suggests that in the planar case the effects of π electron delocalization are much stronger than those of the intra-ring confinement potential. The comparison with experimental determinations of 〈γr〉 offers clear evidence that in solution oligo-p-phenylenes are highly conformationally distorted. An improvement of molecular properties is thus predicted if torsions about inter-ring bonds are hindered by proper substitutions or bridging.

Using data from computed observables of vibrational spectroscopy (frequency, infrared, Raman and hyper Raman intensities) we derive structural criteria necessary to design new organic conjugated molecules with enhanced non linear optical responses. In this work, in particular, we focus on second order hyperpolarizability (γ) and extract from our analysis the structural requirements necessary to reach large negative γ values.

The study of temperature dependent infrared (i.r.) and Raman spectra of alternating ethylenetetrafluoroethylene (ETFE) copolymer suggests that the transition from orthorhombic to hexagonal phases may be driven by the generation and propagation of conformational solitons (gentle mobile chain twist).

It is shown that molecular non linear optical properties can be measured with the vibrational infrared and Raman spectra. Correlations between optical non linearities and structural features are discussed.

The aim of this work is to understand the molecular structural properties which may justify the great observed stability of doped alkoxy polythiophenes. Infrared frequency and intensity spectroscopy and Raman spectroscopy are used as probes. Suitably synthesized oligomers with increasing chain length and preassigned chemical structure have been studied together with several model molecules. The existence of through‐space and through‐bond S‐ ‐ ‐O interactions has been revealed. The extent of the topologically dependent perturbation induced by the charge injection by the oxygen atoms is detected and measured. The inter‐ and intraring delocalizations have been monitored by the observation of the softening of the strongly Raman active ‘‘amplitude mode’’ and by the red shift of the electronic spectra. The conformation of the side chains is trans planar in the solid state and collapses in a liquidlike premelting state before the melting of the crystal.

The temperature-dependent vibrational infrared and Raman spectra of 20% solutions of decylammonium chloride in H2O (D2O) were studied. According to previous work, phases SI and SII were identified in the low-temperature range. Molecular and supermolecular structures were derived. The upper shift (Δν = 12 cm−1) of the Raman-active antisymmetric stretching CH2 mode (d−) and its narrowness are peculiar and specific signals of a specific structure. It is proposed that the phase transition SI SII is originated by the onset of a conformational flexibility generally described as twistons or conformational solitons. No evidence was found that the alkyl residues have librational freedom about their axes.

Frequency and intensity spectroscopies have been used in the reanalysis of the vibrational spectrum (IR and Raman) of alternate copolymers of ethylene and tetrafluoroethylene. A new assignment of the CH stretching fundamental is proposed. The seeming anomalies of the infrared spectrum in the CH stretching range are accounted for in terms of equilibrium atomic charges and charge fluxes. In particular, the analysis of the dichroic ratios shows that there exists a relevant mobility of the electronic charge along the C-C bonds

Recent applications in the field of photonics require materials with a large non-linear response to applied fields. Among the tools that can indicate which organic material has a large hyperpolarizability, there is vibrational spectroscopy. It is shown here that materials with very large Raman intensities have a large, second hyperpolarizability accounted for in terms of relaxation mechanism; it is also suggested that doped materials, which have an anomalously large infrared intensity, can have a large, first hyperpolarizability. Moreover, the relaxation mechanism involved in hyperpolarizabilities can be explained in terms of changes in geometries along the direction of the “effective conjugation coordinate”Я

The intermolecular interactions in amylose/dimethyl sulfoxide (DMSO) complexes are discussed both experimentally and theoretically by means of Raman and infrared spectroscopies. The study is based on a preliminary analysis of well known systems such as pure liquid DMSO or DMSO in mixture with water: for such systems, an analysis of the CS stretching region is carried out both by means of Raman and infrared spectra. In particular, Raman spectra reveal a high sensitivity to the strength and to the type of interaction involving the DMSO molecules. These results, applied to the investigation of amylose-DMSO complexes, show the presence of different hydrogen-bonded complexes which coexist in this compound. In particular, DMSO molecules are identified both on the external surface of the V-amylose helix, where they can interact via one hydrogen bond and in the inner channel of the helix where they can interact via two hydrogen bonds. The present findings open the possibility of applying vibrational spectroscopy to the characterization of inclusion compounds of amylose which are currently being involved in many fields of nanosciences. Copyright © 2009 John Wiley & Sons, Ltd.

The infrared and Raman spectra of oligomeric model molecules of polyparaphenylenevinylene (PPV) and of the polymer in the pristine state, and the infrared spectra of doped or photoexcited PPV are analyzed in terms of the theory of the effective conjugation coordinate (ECC). It is shown that all the spectroscopic observations (frequencies and intensities) are accounted for by ECC theory which shows that most of the observed features are due to the delocalization of π electrons. Measurements of the lower limit of the effective conjugation length and of the molecular chain length are made and the structural relevance of such concepts are discussed in terms of the conformation of the oligomeric or polymeric chain. Evidence is found that the charge carrier produces ‘‘quinoid’’ type defects, hence fully coplanar.

This paper treats the vibrational and UV/visible spectra of oligomers of polyparaphe‐ nylenevinylene (PPV) and lays the background knowledge for the treatment of the spectra and structure of PPV which is treated in the paper that immediately follows. The problem of the molecular conformation of these systems is faced both with MNDO (modified neglect or differential overlap) calculations and with infrared‐Raman experiments. Oligomers are certainly twisted in noncrystalline phases while may approach coplanarity in the solid. Fourier transform Raman spectra are recorded and are interpreted in terms of the recently developed theory of the effective conjugation coordinate.

It is shown that the infrared and Raman spectra of polythiophene, pristine, doped or photoexcited as well as the spectra of the oligomers pristine and doped are accounted for by the effective conjugation coordinate theory. An effective conjugation force constant associated with the delocalization of the π electrons is measured. It is proven that delocalization extends at least over five thiophene rings and that the samples of the polymer consist of a distribution of conjugation lengths with a confinement length of at least five thiophene rings. The infrared spectrum of the doped and photoexcited polymer is consistent with the existence of a bipolaronic conjugational defect confined within ∼5 thiophene rings.

The vibrational dynamics of oligomers of thiophene is treated theoretically and the experimental infrared and Raman spectra are studied with the main purpose to derive information for the interpretation of the spectra of polythiophene. The optimized geometries and the vibrational force field are calculated for the oligomers Thn (n=1, 2, 3, 4, and 6) and the parameters are used for PTh. For PTh and two isotopic derivatives dispersion curves and k=0 phonons frequencies are calculated and a vibrational assignment is proposed.

In the search for experimental evidence for conformational solitons or twistons in polymethylene chains, results from ‘ab initio’ calculations are presented which suggest that just slight distortions from trans planarity of the carbon skeleton of these systems introduce sizeable perturbations in the electronic and dynamical properties of the CH2 groups. The vibrations of these occur at frequencies slightly higher than those of the transplanar structure and overlap with the absorption of the pinned, classical conformational defects such as GG, GTG', end-TG, etc. The experimental observations on selectively deuterated stearic acid are presented and discussed.

Following our previous work in this field it is shown that the vibrational infra-red spectrum indicates that polyoxyethylene, usually in the most stable helical structure (H), transforms into a trans planar structure (T) when in contact with syndiotactic poly(methyl methacrylate) (PMMA). The conversion of solid H to solid T decreases gradually from syndiotactic PMMA to atactic PMMA to isotactic PMMA. A comprehensive interpretation is proposed in order to reconcile the detailed spectroscopic data reported here and the overall morphological descriptions reported by other authors.

Lattice dynamical calculations were performed on poly(vinylidene fluoride) considered in the ideally perfect α and β structures or in a conformationally disordered structure. Head-to-head and GTG′ defects were considered. The conformational soliton proposed by Taylor has been also considered as a cooperative large defect and its spectrum has been calculated. From calculations indications were obtained for the idenfication of infrared or Raman bands originating from the “amorphous” part of the material. The problem of the existence of localized or cooperative conformational defects in this material is presented and information obtainable from the vibrational spectra are discussed.

The interpretation of the infrared and Raman spectra of pristine polypyrrole as 1‐d lattice is presented as the result of lattice dynamical calculations. Geometries and vibrational force fields are derived from semiempirical quantum chemical calculations and/or from the optical spectra of oligomers. This paper lays the background information which are used in the second paper, which immediately follows, where the spectra of the conducting polymer are extensively discussed.

A detailed vibrational analysis of the infrared and Raman spectra of doped and pristine polypyrrole is presented. The theory of the effective conjugation coordinate is applied and fully justifies the observed spectra. The information on the structure and properties of this material derived from the proposed analysis are presented and discussed.

We analyze the infrared and Raman spectra (both experimentally and with the aid of quantum chemical calculations) of a series of polyenals which provide us with the fortunate case of a set of polyene chains with one of the end groups consisting of a CO group which not only does take part in the conjugation but also pulls electrons from the chain making the whole system highly polar thus affecting the vibrational transition moments. In the following we show, for the first time, that it is possible to derive experimental phonon dispersion curves and these prove to be different for each chain length. We support our experimental findings with DFT quantum chemical calculations which reproduce with sufficient accuracy the IR and Raman spectral pattern and at the same time help in disentangling the assignment of the fine structure observed in the experimental spectra.

The photoinduced IR spectrum of electrosynthesized polyfuran is recorded. The observed spectrum is rather more complicated than expected from effective conjugation coordinate formalism. The new experimental data suggest that either the polymer sample consists of bimodal distribution of conjugation lengths or that the charge carrier is highly localized over very few rings

The sections in this article are Introduction Parametrization of Infrared Intensities Internal Derivatives of the Dipole Moment (PR) Atomic Polar Tensors Electrooptical Parameters Equilibrium Charges and Charge Fluxes (ECCF) Conclusion on Intensity Parameters Problems Occurring in the Parametrization Use of Data From Isotopic Species Rotational Corrections Sum Rules Signs of the Dipole Moments Overlay Technique Redundancies Principal Uses of the Different Parametrizations History Transferable Parameters Interpretation Comparison with Quantum Mechanics Calculated Infrared Intensities Calculated PR and their Signs Calculated PX and their Partitions Atomic Charges Use of Intensity Markers for Diagnosis Acidity of Hydrogen Atoms in Hydrocarbons Activation of -Modes A Final Comment Appendices Appendix 1 Background Appendix 2 CCFO Partition of APT Appendix 3 King's Effective Charges and ECCF

We present a simple two-state model that justifies the dependence of first-order hyperpolarizabilities ( β ) of push–pull polyenes on conformational disorder. Particular relevance is given to the calculation of the vibrational properties (i.e. force constants, infrared and Raman intensities) which are used for the evaluation of the vibrational contribution to static molecular hyperpolarizabilities. The theoretical predictions are compared with experimental measurements of the quantities of interest on suitable molecules purposely synthesized.

In this paper, we present a theoretical study, based on quantum chemical “ab initio” calculations, on the structural requirements necessary for obtaining large and negative third order molecular polarizabilities (γ). In particular, we focus on polymethine dyes (H2N–(CH2)n–NH2) of various chain lengths. We show how it is possible to obtain the desired structural data from the frequency and intensity analysis of the vibrational spectra (infrared and Raman). Moreover, the vibrational method allows to calculate the vibrational contributions to molecular polarizabilities and thus permits an estimate of the non-linear optical (n.l.o.) response of the molecules considered. The conclusion that can be drawn is that in order to optimize the results attention must be paid not only to the intrinsic molecular property but also to the mutual arrangement of the molecules in any condensed phase. Our study is completed by the synthesis of one of the molecules studied chosen as a representative of the whole class. In this way, we could experimentally verify the conclusion derived from the theoretical calculations.

A model is presented which allows to obtain a linear relationship between infrared and Raman intensity parameters of the strongest vibrational bands of push–pull conjugated molecules. The results obtained clarify the origin of the exceptionally large values of the vibrational first hyperpolarizability shown by these molecules.

Infrared and Raman spectra of perylene and terrylene computed by ab initio methods at the 3-21G level are presented and discussed. The pattern of the Raman spectrum is very similar to that observed experimentally (even if unscaled frequencies are too high) and characterized by few strong totally symmetric bands; moreover, the agreement between calculated and measured Raman intensities is quite good. Vibrational contributions to second-order molecular hyperpolarizability, γijklr, for the two compounds studied are calculated starting from ab initio Raman frequencies and intensities. The values obtained for the orientation average 〈γ(r〉×=2.6010−35 for perylene and ×1.9010−34 esu for terrylene) are in extremely good agreement with the experimental determination. In the case of perylene we have also calculated the electronic second-order hyperpolarizability, γijkle, with an ab initio finite field method at the same level of approximation (3-21G) as the vibrational analysis. For completeness the case of naphtha...

Vibrational spectra of push–pull polyenes show a peculiar feature namely, in infrared and Raman spectra strong, coincident bands appear, arising from vibrations localised on the polyene bridge. A simple model, based on the introduction of an effective internal field due to the charge transfer between end groups allows the infrared and Raman intensities of these bands to be related.

In this work we present a theoretical justification, based on a two-state model, of the recently observed close resemblance between the molecular first-order hyperpolarizability (${\mathrm{\ensuremath{\beta}}}^{\mathit{e}}$) obtained with traditional experimental or theoretical methods and the vibrational (or relaxation) contribution (${\mathrm{\ensuremath{\beta}}}^{\mathit{r}}$) for several classes of polyconjugated molecules. The vibrational hyperpolarizabilities have been evaluated according to a semiclassical model previously presented by the authors in which molecular polarizabilities are expressed in terms of vibrational (infrared and Raman) intensities. Here we prove that in the case of polyconjugated molecules, the analytic expressions of ${\mathrm{\ensuremath{\beta}}}^{\mathit{e}}$ and ${\mathrm{\ensuremath{\beta}}}^{\mathit{r}}$ are functions of the same physical parameters. This implies that ${\mathrm{\ensuremath{\beta}}}^{\mathit{e}}$ and ${\mathrm{\ensuremath{\beta}}}^{\mathit{r}}$ provide a measure of the same physical property. \textcopyright{} 1996 The American Physical Society.

Experimental data are presented and discussed on the relaxation contribution (β r and γ r ) to first- and second-order molecular hyperpolarizabilities of classes of polyconjugated organic materials. These data are obtained from the measure of classical vibrational observables, i.e., vibrational frequencies, infrared intensities and Raman cross sections. It turns out that the values of β r and γ r are very similar (both in values and trends) to the electronic molecular hyperpolarizabilities β and γ obtained from traditional direct experiments. It is concluded that for the molecular systems considered, β r and γ r may be a good estimate of static, non-resonant β and γ. The justification for such conclusions is that in polyconjugated systems very large electron-phonon coupling takes place such that vibrational displacements are strictly related to and cannot be separated from electronic excitations.

Summary form only given. The experimental and theoretical hyperpolarizabilities (/spl szlig/ and /spl gamma/) of several low band gap organic molecules are studied. These data are compared with the relaxation contributions (/spl szlig//sup r/ and /spl gamma///sup r/) calculated from vibrational observables (i.e. from infrared and Raman frequencies and intensities) on the basis of a model previously proposed by us. In all the cases studied the striking observation is made that the experimental and theoretical /spl szlig/ and (/spl szlig//sup r/ or, /spl gamma/ and /spl gamma//sup r/ are practically identical. These findings suggest that the evaluation of (/spl szlig//sup r/ and /spl gamma//sup r/ from vibrational data of low band gap molecules becomes an alternative way to measure molecular hyperpolarizabilities. The physical basis for this idea and its relevance will be presented and discussed.

Summary form only given. The issue on whether Poliisothionaphtene (PITN) has a quinoid or aromatic structure is still debated. Several quantum chemical calculations have been presented. This work represent an experimental approach to the problem. Several model molecules which force either the quinoid or the aromatic structure have been synthesized. The vibrational spectra (infrared and Raman) have Jeen used as the structural probe; the analysis of the Raman spectra is based on the theory of the Effetive Conjugation Coordinate. The evidence collected suggests that in its gound electronic state PITH has a quinoid structure.

Electro-optical parameters have been determined in terms of equilibrium charges and charge fluxes for cis - and trans -C 2 H 2 X 2 (X=F,Cl) using atomic polar tensors (APTs) obtained from 6-31G* ab initio calculations. On the whole, these results point to a greater similarity between the electronic structures of cis - and trans -C 2 H 2 Cl 2 than between those of the fluorine-containing isomers, the major difference in the latter being due to their equilibrium atomic charges. These conclusions are supported by the better agreement between experimental infrared intensities of the trans -C 2 H 2 Cl 2 isomer and its predicted values evaluated from the experimental APTs of the cis isomer. Finally, the basis set dependence of the standard and corrected Mulliken charges of cis -C 2 H 2 F 2 has been analysed. The similarity between these is only reached when diffuse functions are used.

The activity of a normal mode in vibrational spectra of polyenes (short, long or infinite) can be essentially represented by the quantity δΦ/δяLяi. Φ is the molecular dipole moment μ in IR and the molecular polarizability ((α)) in Raman respectively. я is the “effective conjugation coordinate” and Lяi is the content of in the i-th mode. δ μ /δя vanishes in pristine compounds and is large in doped and photoexcited ones; δ((α))/δя is large for udoped chains and practically vanishing for doped ones. This statement originates from the interpretation of vibrational spectra [1] but is also supported by results of ab-initio calculations made by Villars, Dupuis and Clementi [2].

The experimental observation we wish to explain and which is common in most of the polymethylene systems with no polar substituents is that the absorption intensity in the infrared of the CH2 wagging motions is extremely weak for solid all‐trans chains and becomes much stronger in the liquid phase in which molecules are conformationally distorted. Using current theories for the interpretation of the infrared intensities, it is shown that the observed phenomenon arises from the fact that for all transplanar chains, a sizeable ‘‘σ conjugation’’ along the CC chain takes place. It is shown that ‘‘charge fluxes’’ from second nearest neighbors play the main role in determining such intensity behavior.

The current state of the art in the field of vibrational intensity is reviewed. The parametrisation of the infrared intensities and the physical meaning of the parameters is discussed. A comparison is made of experimental infrared atomic charges with those calculated from quantum-chemical methods. The applications of intensity parameters in spectroscopy and in molecular sciences are presented and discussed.

In the study of compatibility in polymer blends the importance of specific electrostatic interactions is generally acknowledged. What is generally needed are ways to evaluate the tendency of the components to form blends. The existence of positive or negative sites active in the blending process can be indicated by IR spectroscopy through the measure of absolute or relative infrared intensities. Ab initio calculations may be of great help when spectroscopic experimental data are not available.

Summary form only given. Recently, neutral polyfuran (PFu) has been prepared following the cathodic routo by electroreduction of 2,5-dibromofuran using Ni(biPY)/sub 3/ /sup 2+/. The spectroscopic analysis of the PFu samples in the pristine and iodine-doped states indicated that polyconjugation may exist in the polymer. Here, we extend our study of polyconjugation in PFu to the photoinduced infrared absorption spectrum. The formalism of the Effective Conjugation Coordinate which was used in the analysis of pristine and doped material will be used to understand the photoinduced infrared spectrum.

Vibrational spectra (infrared and Raman) of ethylenetetrafluoroethylene copolymers show peculiar characteristics in the CH stretching region: 1. CH 2 stretching bands (of the regular alternating structure) show appreciable frequency shift to higher energies when compared with CH 2 stretching bands of n-alkanes. 2. the IR intensities of the CH 2 stretching bands are very small if compared with the absorptions in the deformation region. 3. the IR CH 2 symmetric stretching band of a spectrum recorded in polarized light on a highly oriented sample shows a dominant component in the polarization direction parallel to the chain axis. We will show in this communication that the data in 1) and 2) can be rationalized in terms of increased polarity of the CH bonds, due to the inductive effect of the fluorine atoms. Observation 3) seems anomalous: it implies that the dipole moment variation induced by CH 2 symmetric stretching has a direction which significantly deviates from the direction along which the vibration takes place (orthogonal to the chain axis). This behaviour can be accounted for in terms of the existence of very large charge fluxes which take place along the CC backbone during CH stretching. This shows the existence of a large electron mobility along σ-bonded chains with highly polarized CC bonds. These data shed further light on the bonding properties of these kinds of polymers and give important information on the use of infrared dichroism in the study of oriented polymers.

The Raman and i.r. spectra in the CH- and CD-stretching region of D -glucose and five selectively deuterated derivatives in the solid state have been recorded. The CH (CD) bonds have different force constants depending on their position and conformation in the pyranose ring and on the dihedral angle HCOH (DCOH). Calculations of the intensities of the i.r. bands confirm these conclusions. Modifications of the force field are proposed that account for the changes in the spectra for solutions in D2O, which are useful for the interpretation of vibrational c.d. spectra.

The CH 2 wagging region in the infra-red spectrum has been investigated for polyethylene single crystals grown from a range of solvents and with a range of characterized crystal habits, for the purpose of identifying ‘fold band(s)’ and studying their variation with crystal habit. Peaks in the region previously identified using subtraction techniques with regular folding at the crystal surface are now revealed directly, using Fourier self-deconvolution. One such peak, at 1342 cm −1 , corresponds in frequency to a band assigned to a ggtgg defect in model systems, suggesting a contribution from this defect to the polyethylene spectra. The wagging mode region shows variations with crystal habit. Furthermore, the decrease in intensity around 1346 cm −1 on either annealing or quenching from the melt supports the assignment to a regular and possibly adjacent fold arrangement. Nevertheless, there appears to be no unique assignment of the wagging modes to one particular type of fold.