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Band alignment transition from type-I to type-II of InP/In 0.48 Ga 0.52 P quantum dots (QDs) is observed by modifying the geometrical factors of the dome-shaped QDs. Strain distribution in InP/In 0.48 Ga 0.52 P QD is calculated using a valence force field (VFF) model. With the strain Hamiltonian from the VFF model, electrical structures of the QDs are obtained using 8-band k•p model. The results from this theoretical study show that the band alignment of the InP/In 0.48 Ga 0.52 P QDs can be tailored from type-I to type-II by controlling the size of the QDs, and flat valence band can be achieved at certain values of height and width of the QDs. In addition, InP/In 0.48 Ga 0.52 QDs of various sizes with the same effective bandgap but different band alignment is observed.

We compare the simplified valence-force model for single-layer black phosphorus with the original model and recent ab initio results. Using an analytic approach and numerical calculations we find that the simplified model yields Young's moduli that are smaller compared to the original model and are almost a factor of two smaller than ab initio results. Moreover, the Poisson ratios are an order of magnitude smaller than values found in the literature.

We have studied, by computer simulation, some static and vibrationnal proprieties of SiGe/Si islands. We have used a Valence Force Field combined to Monte Carlo technique to study the growth of Ge and SiGe on (001)Si substrates. We have focalised on the case of large pyramidal islands presenting (113) facets on the free (001)Si surface with various non uniform composition inside the islands. The deformation inside the islands and Raman spectroscopy are discussed.

The Raman frequency shifts and the depolarization ratio of the Raman lines have been determined for the compounds NaCl. AlCl3 and NOCl. AlCl3 (in the last case with qualitative polarization measurements only). The preparation of pure NOCl. AlCl3 is described in extenso. The properties of the compound finally obtained are different from those given in the literature. NaCl. AlCl3, has to be considered as Na+AlCl4−, and NOCl. AlCl3 as NO+AlCl4−. There is a perceptible interaction between nitrosyl and the chlorines of AlCl4− in the last compound. The properties of NOCl. AlCl3 are intermediate between those for a pure heteropolar compound (NO+AlCl4−) and a pure molecular compound NOCl. AlCl3, being more alike those of the heteropolar form. Force constants have been calculated for AlCl4;−, making use of the Lechner formulae and of those for a Urey-Bradley field and also of those for the orbital valence force field of Heath and Linnett.

Powell c.s. deduced from an X-ray study that solid PCl5 has to be considered as [PCl4+] [PCl6−]. From the distances between P and Cl in PCl4+ and in PCl6− given by the authors, force constants fPCl4+ and fPCl6− have been calculated using Badger's rule. From these f values and by a comparison with the results of a similar calculation for SiCl4 it follows that the strongest lines of the Raman spectrum of PCl5, namely 358(15) and 451 (7), belong to v1(PCl6−) and v1(PCl4+) respectively. With these frequencies known, it is possible to make an estimate of the frequencies to be expected for the other Raman-active vibrations of both ions. A probable assignment of Raman shifts to vibrations of PCl4+ and PCl6− is given. Force constants have been calculated for both ions, using formulae based on Nath's force field and on the orbital valence force field introduced by Heath and Linnett, Probable frequency values: PCl4+ 173, 244, 451, 627; PCl6− 244, 285, 358.

The infrared and Raman spectra of CH3HNCOCOOCH3, and the nitrogen-deuterated derivative have been recorded; the fundamentals have been assigned and a valence force field has been calculated.

The infrared and Raman spectra of (CH3)2NCOCOOCH3 and KOOC COOCH3 have been recorded, the fundamentals have been assigned, and a valence force field has been calculated.

The possibility of using the PM5 semiempirical method and the LADY program for calculations of the vibrational properties and thermodynamic characteristics of copper carbonates, malachite and azurite, was considered. The infrared and Raman spectra of these minerals were calculated using the valence force field model of the theory of crystal lattice dynamics with varying force constants. The results closely agreed with the calorimetric and spectroscopic experimental data.

Microscopic phonon theory of semiconductor nanocrystals (NCs) is reviewed in this paper. Phonon modes of Si and Ge NCs with various sizes of up to 7 nm are investigated by valence force field theory. Phonon modes in spherical SiGe alloy NCs approximately 3.6 nm (containing 1147 atoms) in size have been investigated as a function of the Si concentration. Phonon density-of-states, quantum confinement effects, as well as Raman intensities are discussed.

A theoretical approach to the lattice dynamics of Si 1 - x Ge x alloys within a valence force field framework is discussed. A modified Keating model, the anharmonic Keating, was employed to perform supercell calculations in order to investigate accurately the three Raman active optical phonon modes. Theoretical results on both relaxed and strained SiGe samples are shown. A detailed study of the biaxial strain-induced shift of phonon modes of epitaxial SiGe alloys has been performed in all the composition range. Furthermore, a comparison of experimental data with the model results on phonon strain shift coefficients will be also discussed.

In an approximation of the generalized valence force field, the frequencies and forms of the normal vibrations of the free molecule of spiroanthraceneoxazine (SAO) are calculated. The vibrational spectra of SAO are measured: the IR absorption spectra in an NaCl disk and the Raman spectra in a KBr disk. The calculated and experimental data were correlated with the aid of a method of refined initial data. The results obtained agree with the calculated and experimental spectra of model and related compounds.

Calcium chloride (40CaCl2 and 44CaCl2) and bromide (40CaBr2) complexes of 4,13-diaza-18-crown-6 (DA-18C6) were investigated using IR and Raman spectroscopy and normal coordinate analysis (NCA). Calcium isotopic substitution was used to determine the valence force field of the DA–18C6–CaCl2 complex (C2h symmetry). Practically no change in the vibrations of the macrocyclic ligand were observed upon complex formation, indicating the absence of conformational distortion.

The Raman wavenumbers of bicyclo[2.1.0]pentane (BCP), isolated in a low-temperature matrix, are presented and assignments for all vibrational fundamentals are proposed. The molecular structure of BCP is calculated by means of semi-empirical quantum-mechanics and a normal coordinate analysis of the strained bicyclic system is performed in internal coordinates in terms of a valence force field.

A detailed study of the fundamental internal modes of the 1,2,4,5-tetrabromobenzene crystal has provided assignments of Raman-active modes consistent with polarized single-crystal measurements. A normal-mode calculation based on a valence force field derived from brominated and chlorinated benzenes is found to be in excellent agreement with the assignments. Additional bands arising from anharmonic interactions of the fundamentals are also assigned.

A normal mode analysis of syndiotactic poly(1-butene) of form I having (TTGG)2 conformation was made in accordance with the valence force field derived by Holland-Moritz for isotactic poly(1-butene) of form I. The assignments were made successfully using polarized infrared and Raman spectra. Based on the assignments, spectral characters in the melt and the low temperature were investigated. The infrared and Raman spectra did not change in the melt but the CCH bendings of the spectra in the low temperature were sensitive to the conformation.

In the early stages of highly mismatched heteroepitaxy (e.g. for InAs deposited on GaAs) self assembled dots (SAD) with a sharp distribution in sizes appear as soon as the coverage exceeds a critical value. We show that this phenomenon is determined by the preliminary growth of 2D platelets which act as precursors for the formation of 3D coherent islands. The argumentation is based on a total energy calculation using a valence force field approach for the elastic part (including dimers), the residual surface contribution (dangling bonds) being added separately. It is demonstrated that the existence of a critical coverage is related to the interaction between platelets. The proposed mechanism provides an appealing explanation for the fairly good calibration of the observed 3D islands. Moreover, our description appears to give the right order of magnitude for the 2D platelets size, the early quantum dots size, the width of the Gaussian distribution, the magnitude of the critical coverage, and finally the fact that such a phenomenon is not observed at lower values of the mismatch.

Infrared and Raman spectra of polycrystalline Y2O3 as well as polarized Raman spectra of Y2O3 single crystals have been measured. A complete assignment of the bands is proposed. A normal coordinate analysis using a generalized valence force field enabled us to fit the observed frequencies with a satisfactory accuracy (3.5%). The calculated force constants are discussed and compared with those of α-Al2O3 exhibiting the same atomic coordination.

Fourier-transform infrared and Raman spectra of l -Ala- l -Ser, d -Ala- l -Ser and l -Ser- l -Ala were recorded, and significant differences were found between the spectra of these dipeptides. In order to interpret these differences, the normal vibrations of l -Ala- l -Ser, d -Ala- l -Ser, l -Ser- l -Ala and d -Ser- l -Ala were calculated from an empirical general valence force field and molecular geometries calculated by MM2 methods. Initial values of the force constants for the normal coordinate analysis were transferred from the known spectroscopic empirical force fields of alanine, serine and poly( l -alanine). Then, a partial refinement of force constants was performed to improve the fit to the experimental spectra of l -Ala, l -Ser and some of their deuterated analogues. Differences were obtained between the calculated spectra of ll and dl derivatives; the significant differences between the experimental spectra, however, could be reproduced with limited success, suggesting that the latter may be due in part to differences in crystal rather than in molecular structures.

A normal coordinate analysis has been performed for H10Si10O15 by applying the modified general valence force field determined for H8Si8O12. Using group theory allows a quantitative correlation of all infrared and Raman active fundamentals of the two molecules, for which the experimental spectra are presented.

Infrared and Raman spectra were obtained for 2, 3, 3-trimethyl-1-butene, and a vibrational assignment was made with the aid of normal coordinate calculations. Molecular mechanics calculations were also made to determine molecular parameters of the stable conformation. Values for the force constants of a forty-one parameter modified valence force field were obtained that will be used for other 2-methyl-1-alkenes that contain substituted methyl groups.

Results are presented of an optimized valence force field of the dihydridoosmium(II) complex [(mes)OsH2(CO)] (mesC6H3(CH3) 3-2,4,6) in which the ring was treated as a point mass. The Raman and IR spectra of metal-coordinated mesitylene are given and the results of normal coordinate analysis of the arene described. From the results, a modified general valence force field including the whole ring ligand has been calculated. The results are discussed, and compared with those of the model with point mass approximation.

The IR and Raman spectra of the ten bromo-iodo-rhenates(IV) [ReBrnI6-n]2-, n = 0 -6 , including the geometrical isomers for n - 2,3,4, have been recorded at 80 K. The vibrational spectra are completely assigned according to point groups Oh, D4h, C4v, C3v, and C2v, as supported by normal coordinate analyses based on a general valence force field. Due to the different mms-influences Br < I in asymmetric axes Br•-Re-I', the Re-I' bonds are strengthened and the Re-Br• bonds are weakened, as indicated by valence force constants, for Re-I' on average 8,5% higher and for Os-Br• 8,3% lower, as compared with the values calculated for symmetric I-Re-I and Br-Re-Br axes, respectively

Valence force field model has been constructed for lattice dynamics of ?-Si3N4. The values of force constants were determined by fitting the phonon frequencies of ? point to experimentally observed Raman spectra. The phonon dispersion curves in several principal directions in Brillouin zone, the total density of states and some phonon related physical properties were calculated.

[TcX6]2−, X = Cl,Br, reagiert bei Raumtemperatur mit Trifluoressigsaure unter Bildung der kantenverknupften Dioktaederanionen [Tc2X10]2−, deren IR- und Raman-Spektren entsprechend der Punktgruppe D2h zugeordnet werden. Basierend auf den kristallographischen Daten isostruktureller Osmiumkomplexe und unter Verwendung des allgemeinen Valenzkraftfeldes, werden fur Decachloro- und Decabromodi-technetat(IV) Normalkoordinatenanalysen durchgefuhrt, die eine gute Ubereinstimmung der berechneten Frequenzen mit den beobachteten Banden aus den IR- und Raman-Spektren ergeben. Die festere Bindung terminaler im Vergleich zu verbruckenden Liganden spiegelt sich in den Valenzkraftkonstanten wider: fd(TcXt) > fd(TcXb). Preparation, Vibrational Spectra and Normal Coordinate Analysis of Decahalogenoditechnetates(IV), [Tc2X10]2−, X = Cl, Br The reaction of [TcX6]2−, X = Cl, Br, with trifluoroacetic acid yield at room temperature the edge-sharing bioctahedral anions [Tc2X10]2−, which IR and Raman spectra are assigned according to point group D2h. Using the crystal data of isostructural osmium complexes a normal coordinate analysis based on a general valence force field has been performed for [Tc2X10]2−, revealing a good agreement of the calculated frequencies with the bands observed in the IR and Raman spectra. The stronger bonding of the terminal as compared to the bridging ligands is shown by the valence force constants, fd(TcXt) > Fd(TcXb).

From the most precise experimental measurements available from the gas phase for the three vibrational wavenumbers of P 4 , the primary stretching force constant f r = 2.06 mdyn A −1 and two stretch—stretch interaction constants have been evaluated using a simple valence force field. The positive value of f rr 1 and negative value of f rr are confirmed and the value of f r is found to be significantly smaller (15% and 7% respectively) than the corresponding values calculated from the infrared spectra of solutions of phosphorus in carbon disulphide reported in the literature.

A complete interpretation of the benzylidenemethylamine vibrational spectrum has been carried out on the basis of normal coordinate analysis. A valence force field refined on three isotopic species of benzylidenemethylamine has been determined. The obtained force constants have been used to calculate the vibrational spectra of benzylideneaniline (C6H5CHNC6H5) and its fluorosubstituents (4FC6H4NCHC6H5, C6F5 N  CHC6H5, C6H5NCHC6F5 and C6F5NCHC6F5). The normal coordinate analysis has been carried out using the new experimental data from the IR and Raman spectra of the parent molecule, its partially and perdeuterated isotopomers and 15N labelled species of benzylideneaniline [1] and 15N fluorosubstituents [2]. The influence of the substitution of H atoms of the phenyl rings by one F atom on the azomethine group modes has been studied.

A general procedure is described for vibrational analysis, using an ab initio force constant matrix which is transformed into the generalized valence force field. A method using numerical least-square fitting and redundancy elimination is proposed to determine the valence-symmetry coordinates in terms of the internal coordinate displacements. The computer program was customized to simplify the data deck construction and to input most of the data directly from the GAUSSIAN 8X output file.

Raman spectra of sulfur vapor at 620°C under 530.8 nm excitation basically consist of resonance Raman spectra of S4 molecule. Only the three symmetric modes are observed, valence force field calculations confirm the trans planar structure C2h of S4.

Raman spectra (1 600 - 100 cm-1) of liquid S2O5F2 and Se2O5F2 and infrared spectra of liquid and gaseous S2O5F2 were measured. A modified general valence force field was used for their interpretation by normal coordinate analysis. Refinement of the number of lines in the Raman spectrum of S2O5F2 by means of numerical separation of the overlapping bands led to the conclusion that liquid S2O5F2 consists at least of three rotamers at room temperature.

A general valence force field for 1-methylthymine (1MeT) in the isolated state has been unequivocally determined from the calculation of both the frequencies and the relative ultraviolet resonance Raman intensities arising from the first lowest lying vibronic transitions. In a second step, the normal modes were derived for the crystalline state using the previously determined in-plane force field and an out-of-plane force field was deduced.

Infrared and Raman spectra were obtained for 4,4-dimethyl-2-pentyne. Vibrational assignments were made with the aid of normal coordinate calculations that utilized a 20-parameter modified valence force field, with the values of the force constants being transferred from 4-methyl-2-pentyne. Molecular mechanics calculations were also made in order to calculate the molecular geometry and heat of formation.

Infrared and Raman spectra were obtained for 3-methylbut-1-yne and 3,3-dimethylbut-1-yne. Vibrational assignments were made with the aid of normal coordinate calculations that utilized a 27-parameter modified valence force field. The average difference between the observed and calculated wavenumbers was 6.0 cm −1 for the two molecules. Molecular mechanics calculations were also done for both compounds.

A method is presented by which ab initio (or empirical) force fields and structures can be converted to molecular mechanics energy parameters. Using Cartesian coordinates, the effect of van der Waals and other nonquadratic interactions is eliminated from the original spectroscopic force field, and molecular mechanics force constants and reference geometry parameters are derived. The computed parameters yield molecular structure and vibrational frequencies that are identical to the original ones. The transformation produces a complete general valence force field, which in most cases is impractical, and a procedure to reduce the number of force constants is therefore described. Different ways of applying the transformation are outlined.

In this work, a complete assignment of Raman and IR modes is reported for both poly(thienylene vinylene) and poly(furylene vinylene) whose chains are composed of an alternation of aromatic rings and vinyl groups. In order to achieve these attributions, we have developped a valence force field model. The vibrations of an aromatic ring show some similarities in a series of compounds with the same cycle. So the same set of parameters is used to calculate vibrational modes for both polymers and model compounds such as trans-bis(2-thienyl)ethylene, a molecule composed of two thiophene rings separated by a vinyl group. Therefore, we present an experimental comparison between Raman spectra of poly(thienylene vinylene), thiophene and trans-bis(2-thienyl)ethylene, and the assignment of the vibrational modes in the latter molecule is also discussed.

The Raman spectra of liquid (CH 3 ) 4−m Si(CD 3 ) m (m=0-4), (CH 2 D) 4−n Si(CH 3 ) n and (CHD 2 ) 4−n Si(CD 3 ) n (n=0-3) were recorded from 3200 to 50 cm −1 . Normal coordinate analyses were made using both a unique internal valence force field (IVFF 1) for all 13 isotopomers and 13 slightly modified IVFF 2s for each isotopomer, including torsional modes in each case. Vibrational assignments were made using the potential energy distributions and eigenvectors in addition to the depolarization ratios, the IR spectra and the Teller-Redlich product rule

The Raman and infrared spectra of N,N-diethylformamide, N,N-diethylacetamide, N,N-diethylchloroacetamide and N,N-diethylpropionamide were measured. Raman polarization measurements were also made. A normal coordinate analysis was carried out for N,N-diethylformamide, N,N-diethylacetamide and N,N-diethylchloroacetamide using a 63-parameter modified valence force field. The force constants were refined in an overlay least-squares technique using vibrational frequencies of the molecules to obtain a converged set of meaningful force constants. The reliability of the force constants so obtained was tested by making a zero-order calculation for N,N-diethylpropionamide. The potential energy distributions and eigenvectors calculated in the process were used to make unambiguous vibrational assignments.

FT-IR and Raman spectra of S-methyl-N,N-dimethylmonothiocarbamate and its d 3 -, d 6 -, d 9 -, and 13 C-substituted isotopomers have been recorded and analysed. Normal coordinate calculations were performed to support the assignment and to derive a simplified valence force field which would be characteristic of the monothiocarbamate moiety, =N(CO)S-, and is consistent with the known bond length vs force constant correlations.

The lattice dynamics of alkali metals is investigated on the basis of a phenomenological model which is consistent with the translational symmetry of a lattice. The potential energy is considered due to (1) ion-ion and (2) ion-electron interactions. The contribution to ion-ion interaction is evaluated applying the valence force field. The contribution to the potential energy from ion-electron interaction is considered through the screened Coulomb potential. The theoretical model developed is employed to compute the phonon dispersion curves of Na, K, Li, Rb, and Cs. Computed phonon frequencies are used to interpret the Debye characteristic temperatures at different temperatures. The calculated results for phonon dispersion curves and Debye characteristic temperatures compare well with the experimental ones. Die Gitterdynamik von Alkalimetallen wird auf der Grundlage eines phanomenologischen Modells untersucht, das mit der Translationssymmetrie eines Gitters konsistent ist. Die potentielle Energie wird in Form von (1) Ion-Ion- und (2) Ion- Elektron-Wechselwirkung berucksichtigt. Der Beitrag der Ion-Ion-Wechselwirkung wird durch Benutzung des Valenzkraftfelds berechnet. Der Beitrag zur potentiellen Energie aus der Ion-Elektron-Wechselwirkung wird durch ein abgeschirmtes Coulombpotential berucksichtigt. Das entwickelte theoretische Modell wird benutzt, um die Phonondispersionskurven von Na, K, Li, Rb und Cs zu berechnen. Die berechneten Phononenfreqiemzem werden benutzt, um die charakteristischen Debye-Temperaturen bei verschiedenen Temperaturen zu interpretieren. Die berechneten Ergebnisse fur die Phononendispersionskurven und die charakteristischen Debye-Temperaturen stimmen gut mit experimentellen Ergebnissen uberein.

In this work, we report experimental Raman and IR results obtained on two different polymers composed of heteroaromatic rings separated by a vinyl group, namely poly(thienylene vinylene) (PTV) and poly(furylene vinylene) (PFV). PTV and PFV exhibit a rather similar behaviour and, in particular, in both cases the observed Raman bands undergo a slight shift when the excitation wavelength is changed from 676.7 to 457.9 nm. By using a dynamical model based on valence force field calculations, we have assigned all IR and Raman modes. In order to obtain a good set of force constants, we started calculations by considering those of polythiophene and, also, we used a model compound such as trans -bis(2-thienyl)ethylene. It was found that the numerical values given for these force constants are consistent with the electronic structure usually assigned for these polymers.

The Raman scattering and infrared absorption spectra of dehydrated bare NaEMT and KEMT zeolites were recorded in the mid- and low-frequency region. Molecular dynamics calculations based on a simplified general valence force field, the cation framework and cation—cation interactions reproduced the main structural and dynamic properties of the Na 20 EMT and K 20 EMT zeolites. The flexibility of the inner void space was studied by considering the diameter and area of the windows connecting two adjacent medium or large cages.

The characteristic peaks, A at 211 and A * at 216 cm −1 , in the Raman spectra of layered crystalline GeSe 2 have been studied by a model calculation using a valence force field and bond polarizability (VFF-BP). The A phonon is extended along the GeSe 4 tetrahedral chain, while the A * phonon is quasi-localized at the edge-sharing GeSe 4 tetrahedra. An extended VFF-BP model including interlayer interactions between Se atoms is proposed to understand the peculiar weakness of the A * Raman intensity.

Die Raman-Spektren der durch Umsetzung von Os16O4 und Os18O4 mit BCl3 dargestellten Isotopomeren Os16OCl4 und Os18OCl4 zeigen starke Isotopenverschiebungen fur die OsO-Valenzschwingung v1(A1) von 1 026 auf 973 cm−1 und fur die OOsCl-Deformationsschwingung v8(E) von 264 auf 253 cm−1. Fur die vollstandige Zuordnung aller beobachteten Frequenzen sind Polarisationsmessungen und eine Normal-koordinatenanalyse auf der Grundlage des allgemeinen Valenzkraftfeldes durchgefuhrt worden. Raman Spectra and Normal Coordinate Analysis of the 16O and 18O Isotopomeres of Tetrachlorooxoosmium(VI), OsOCl4 The Raman spectra of the isotopomers Os16OCl4 and Os18OCl4 prepared by reaction of Os16O4 and Os18O4 with BCl3 exhibit strong isotopic shifts of the OsO stretching frequency v1(A1) from 1 026 to 973 cm−1 and of the OOsCl bending vibrations v8(E) from 264 to 253 cm−1. The complete assignment of all observed frequencies is achieved by polarization measurements and a normal coordinate analysis based on the general valence force field.

Phonon modes and Raman intensities of Ge quantum dots (QDs) with two different types of surfaces, a free standing surface or a fixed surface, in a size range from five atoms to 7 nm in diameter, are calculated by using a microscopic valence force field model. The results are compared, and the effects of surfaces on phonon properties of QDs are investigated. It is found that phonon modes and Raman intensities of QDs with these two different types of surfaces have obvious differences which clearly reveal the effects of the surfaces of QDs. The calculated results agree with existing experimental observations. We expect that our calculations will stimulate more experimental measurements on phonon properties and Raman intensities of QDs.

The breathinglike phonon modes of multiwalled carbon nanotubes are studied within a valence force field model for nanotubes with two and three layers of armchair type and within a continuum model for nanotubes with a large number of layers. A bond-polarizability model is used to calculate the nonresonant Raman intensity of the breathinglike modes. It is obtained that among all breathinglike modes of a given multiwalled tube, the in-phase one has a maximal intensity. The predicted intensity of the breathinglike modes is compared to available low-frequency experimental Raman data. Special attention is given to the comparison with Raman data on double-walled carbon nanotubes.

Beim Erhitzen des Tetraethylammonium-Salzes (TEA)2[TcBr6] mit Trifluoressigsaure entsteht das flachenverknupfte Bioktaederanion [Tc2Br9]−, dessen Schwingungsspektrum entsprechend der Punktgruppe D3h zugeordnet wird. Die auf der Grundlage des allgemeinen Valenzkraftfeldes durchgefuhrte Normal-koordinatenanalyse ergibt eine gute ubereinstimmung der berechneten Frequenzen mit den beobachteten IR-und Raman-Banden. Wegen der festeren Bindung der terminalen im Vergleich zu verbruckenden Liganden ist die Valenzkraftkonstante fd(TcBrt) = 1,045 deutlich groser als fd(TcBrb) = 0,80 mdyn/A. Preparation, Spectroscopic Characterization and Normal Coordinate Analysis of Nonabromoditechnetate(IV), [Tc2Br9]−. On heating the tetraethylammonium salt (TEA)2[Tc2Br6] with trifluoroacetic acid the face-sharing bioctahedral anion [Tc2Br9]− is formed, which vibronic spectrum is assigned according to point group D3h. Normal coordinate analysis, based on a general valence force field has been performed, resulting in a good agreement of calculated frequencies with the observed IR and Raman bands. Due to stronger bonding of the terminal as compared to the bridging ligands, the valence force constant fd(TcBrt) = 1.045 is significantly higher than fd(TcBrb) = 0.80 mdyn/A.

We study the low-frequency region of the Raman spectra of infinite bundles of identical single-walled carbon nanotubes within a Valence force field model of the lattice dynamics and a bond-polarizability model for the Raman intensity. It is obtained that two breathinglike phonon modes are present in such bundles for each tube type. Based on this prediction, an alternative interpretation of the experimental Raman spectra is proposed. In particular, an explanation is given for the appearence of resonant Raman lines that are predicted as nonresonant within the noninteracting tube picture.

An empirical valence force-field has been obtained for an ideal two-dimensional crystal of graphite. This force field is the generalization to the infinite case of the force field developed by Ohno (in K. Ohno, J. Chem. Phys. 95 (1991) 5524; K. Ohno, J. Mol. Spectrosc. 72 (1978) 238) for simple Polycyclic Aromatic Hydrocarbons (PAH). Based on classical dynamical calculations we have clarified the origin of the Raman bands observed in PAH and have rationalized their correlation with the Raman features observed in graphitic materials with different degree of purity and crystalline order.

We have studied the growth of lattice mismatched semiconductors through the association of the Monte Carlo technique and the Valence Force Field (VFF) approximation. The Monte Carlo technique monitors the atomic motion in the deposited layer using the Arrhenius law and taking into account the impingment of atoms from the gas phase, intralayer and interlayer migrations of atoms and evaporation from the surface. The VFF approximation is used as an energy model to determine the local strain and stress inside the deposited layer by minimizing the total energy. This is performed after each single atomic motion. The strain is assumed to enhance the atomic motion by lowering the activation energy barrier related to the particular event. Results concerning the case of large lattice mismatches are presented. It is observed that the growing surface becomes rapidly rough, showing grooves with (111) facets. The strain relaxation occurs as a result of this roughening and allows the determination of the critical thickness. At higher lattice mismatches, it is seen that the layer orientation changes from(100) to (111) from the beginning.

IR and Raman spectra of benzophenone and several of its isotopomers (d5−, dl0−, 13C- and 13Cd5-benzophenone) are the experimental basis for the normal coordinate analysis. The possibility of determining the conformation of the benzophenone molecule in solution from its vibrational spectrum is considered carefully. The dihedral angle between the central part of the molecule and the phenyl ring has been determined by fitting the calculated to the observed spectra. The final force field for the molecule was obtained for the dihedral angle of 35°.