Bond Force Constants Research Articles

Lattice-dynamical calculations of crystalline thiourea

The vibrational spectra of the para- and ferroelectric phases of thiourea are interpreted by a lattice-dynamical calculation using atom-atom interactions and the multipole expansion. In both phases the soft mode is calculated in the correct species with a satisfactory frequency. The harmonic dispersion curves for the paraelectric phase are also calculated. The crystal energy and its distribution into different kinds of interactions is discussed. Energy and force constants for the hydrogen bonds are obtained.

Ab-initio calculations of the electronic structure and properties of the diatomic zinc monohalides ZnX (X=F, Cl, Br, I)

Hartree-Fock and configuration-interaction Pseudopotential calculations of the electronic structure and properties of the diatomic zinc monohalides ZnF, ZnCl, ZnBr and ZnI were carried out using a modified version of Pople's SCF program GAUSSIAN 86. Predictions were made for the as yet unmeasured bond lengths and dissociation energies of these species. The calculated bond force constants and vibrational frequencies for ZnCl and ZnI agree well with those obtained experimentally from vapour phase UV emission spectra and from matrix-isolation Raman studies. In the case of ZnBr, the vapour UV and matrix Raman values are very different, and neither agrees well with the calculated value. The fact that the calculated values for the zinc halides show the expected trend from the fluoride to the iodide suggests that neither experimental value for ZnBr is correct.

Quantum-chemical study of the force constants of CH bonds in molecules with three-membered rings

We have considered the effect of the completeness of the basis set on the accuracy of nonempirical calculations of force constants (KCH). We have studied the trends in the value of KCH as a function of the nature of the hetero-atom in saturated and unsaturated rings. On the basis of estimated values of the “orbital strengths” conclusions have been drawn about the substantial contributions from the inner MO in determining KCH. A relation has been obtained and analyzed between KCH and the gradient of the electric field at the proton. Comparison with the previously established relation between KCH and the 2JCH SSIC [spin-spin interaction constants] has led to conclusions about the common character of the electronic interactions which determine the characteristics listed.

Vibrational spectra of aquadioxotetra; peroxodivanadates(V) M2[V2O2(O2)4(H2O)]·xH2O (M = N(CH3)4, Cs)

The infrared and Raman spectra of M2[V2O2(O2)4(H2O)]·xH2O and M2[V2O2(O2)4(D2O)]·xD2O (M = N(CH3)4, Cs) were measured. In the region of the vanadium-oxygen stretching vibrations, the spectra were interpreted based on normal coordinate analysis, employing empirical correlations between the bond lengths and force constants.

Similarity transference of molecular parameters. II. The bond distances, force constants and polar tensors of HC3N and HC5N

The similarity transference procedure is extended to the calculations of the geometries and vibrational frequencies of HC3N and HC5N. Similarity models are constructed using the experimental and STO-3G molecular orbital values of the bond distances and force constants of the HCN, C2H2, CH3CN, C4H2, CH3CCH, and C2N2 reference molecules. Simple linear regression calculations based on these similarity models and using STO-3G values of the bond distances and force constants of HC3N result in estimates of the experimental bond distances and frequencies which have root mean square errors about an order of magnitude smaller than the one for the molecular orbital values. Similarity models for the bond distances and vibrational frequencies and intensities of HC5N are also reported.

Preresonance Raman studies of metal-to-ligand charge transfer in (NH3)4Ru(2,2'-bipyridine)2+. In situ bond length changes, force constants, and reorganization energies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreresonance Raman studies of metal-to-ligand charge transfer in (NH3)4Ru(2,2'-bipyridine)2+. In situ bond length changes, force constants, and reorganization energiesStephen K. Doorn and Joseph T. HuppCite this: J. Am. Chem. Soc. 1989, 111, 13, 4704–4712Publication Date (Print):June 1, 1989Publication History Published online1 May 2002Published inissue 1 June 1989https://doi.org/10.1021/ja00195a025RIGHTS & PERMISSIONSArticle Views314Altmetric-Citations54LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

AB initio force constants: a cautionary tale concerning nitrogen oxides

Quadratic, cubic and some quartic force constants have been calculated for NO +, NO and NO − using a variety of theoretical procedures ranging from 3–21G/SCF to 6–311G (2 df)/MP4SDTQ. Results are of uneven quality, and vary far more with the size of basis and type of theoretical treatment than do the bond lengths. Greater accuracy is obtained if the experimental bond length, rather than the optimized value, is adopted as the reference geometry. It appears that the influence of single and triple excitations on both bond lengths and force constants may be overestimated by fourth-order perturbation theory. There is a dramatic variation in the degree of spin contamination of the UHF wavefunction with bond length for NO; all force constants calculated at any correlated level are of very poor quality, and most are ludicrous. Spin contamination is not serious for either CF (isoelectronic with NO) or NO −. Diffuse functions make an appreciable difference to the force constants calculated for NO −. Force constants obtained at the SCF level using the 3–21G, 6–31G, 6–31G( d), DZ and DZP basis sets are reported for NO 2 + , NO 2 and NO 2 −. Results are again of disappointingly variable quality. There is no consistent scale factor applicable either to a particular basis or to a particular type of force constant. The 3–21G basis is less reliable than the others, and its use is not recommended, while the DZ basis gives the most accurate results overall.

Hydrogen-related center with tetrahedral symmetry in ion-implanted silicon.

The effect of uniaxial stress on a local vibrational Si-H stretching mode observed at 2223 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in proton-implanted silicon has been studied by means of infrared-absorption spectroscopy. It is found that the defect responsible for the 2223-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ line has a tetrahedral point group. Measurements on samples implanted with hydrogen and deuterium reveal that the defect involves more than one hydrogen atom. A detailed analysis based on the valence-force approximation indicates that the line is associated with the hydrogenated vacancy or with monosilane located at the interstitial tetrahedral site. The stress-induced splittings of the line can be analyzed with a single parameter which describes the change in the effective force constant of the Si-H bond when uniaxial stress is introduced parallel to the bond.

Etude comparative des hexahydrido-et des hexadeuteridoaluminates de lithium et de sodium. I - Spectres raman et infrarouge de Li 3-et Na 3AlH 6, et Li 3AlD 6

Raman and Infrared spectra of Lithium and Sodium hexahydrio- and hexadeuteridoaluminates Li 3AlH 6, Na 3AlH 6 and Li 3AlD 6 have been investigated in order to study metal-hydrogen interactions. A vibrational analysis has been performed. Several force field models (Urey-Bradley, Orbital Valence force field, Shimanouchi, Murrell).have been used in order to compute the force constants of Al-H bonds. No significative difference has been observed between the results obtained from the various models, and the environnement of aluminum has been thus well determined : AlH 6 3− ions form an almost perfect octahedron in Li 3AlH 6 and a distorted one in Na 3AlH 6.

Ab initio study of neutral O 2, SO, S 2, C 2H 2 and their mono- and dications

For the twelve title species, the bond order according to Mayer's definition, the Mulliken overlap population and the force constants are determined using the minimal STO-3G, split-valence 3-21G and 6-31G* (5 d) basis sets. In general all these properties increase with increasing formal charge for each diatomic species. In contrast, the internuclear distances decrease with increasing formal charge. These findings indicate that the outer electrons in the three neutral diatomic species reside in antibonding orbitals; removing them results in triple bonds in the dications which are all predicted to be stable in their ground states in spite of the electrostatic repulsion. The best predictions for the unknown internuclear distances in the ionic ground states are: r e(O 2 2+) = 1.046; r e(SO 1+) = 1.411; r e(SO 2+) = 1.359; r e (S 2 1+) = 1.800 and r e(S 2 2+) =1.732 Å. For acetylene, the behaviour on removal of the electrons is opposite to that observed for the diatomics: the bond order, overlap population and force constants all decrease with increasing formal charge. Both the acetylenic cation and dication are predicted to be stable, linear species in their electronic ground states with r e(CC) = 1.247 and r e(CH) = 1.076 Å for the monocation and r e(CC) = 1.326 and r e(CH) = 1.116 Å for the triplet dication. Using the SCF optimized structures, the total energies for the species were computed at the CISD and CISD-Q levels. These lead to predicted second ionization potentials of about 24.1, 19.1, 16.6 and 19.9 eV for O 2, SO, S 2 and C 2H 2, respectively.

Synthesis and vibrational (IR and Raman) spectroscopic study of triangular thio-complexes [Mo 3S 13] 2− containing 92Mo, 100Mo and 34S isotopes

The triangular anionic thio-complex [Mo 3S 13] 2− has been obtained by the reaction of the triangular molybdenum thiobromide Mo 3S 7Br 4 with an aqueous solution of S x 2−. Starting from compounds containing 92Mo, 100Mo and 34S isotopes, the following thio-complexes have been obtained: [ 92Mo 3S 13] 2−, [ 100Mo 3S 13] 2−, [Mo 3 34S 13] 2-, [Mo 3( μ 3-S)( μ 2-S 34S) 3( 34S 2) 3] 2− and [Mo 3( μ 3- 34S)( μ 2- 34SS) 3(S 2) 3] 2−. Along with the nucleophilic substitution of the Br ligands by the terminal S 2 ligands, elimination—addition of sulphur in μ 2-S 2 ligands also takes place. This allows preparation of thio-complexes containing μ 2- 34S 32S ligands. IR and Raman spectra of the thio-complexes have been studied, normal vibrations have been calculated and the bond force constants determined.

Temperature dependence of the elastic modulus of crystalline regions of Poly(ethylene terephthalate)

Abstract The temperature dependence of the elastic modulus E1 of crystalline regions of poly(ethylene terephthalate) (PET) in the direction parallel to the chain axis has been investigated by x-ray diffraction. The axial chain contraction coefficient is constant from 25°C to 200°C, and correspondingly the value of E1 (108 GPa) remain unchanged up to 215°C. This is in contrast with the temperature dependence of E1 values of various polymers previously reported. It is considered for PET that the axial thermal molecular motions which cause the decrement of E1 do not take place in the crystalline regions, and that the force constant of bond stretching and that of bond angle bending are constant over both the temperature and the stress range studied. It is reasonable to conclude that the mechanical structure of drawn PET is composed of the series model.

The Effects of Ring Sobstitijtioh oh the Infrared Spectra of Arentricarbonylchromium Complexes

Abstract The carbonyl region infrared spectra of a large number of arenetricarbony, chromium complexes containing diverse functionality have been determined. The force constants of the CO bond calculated using the Cotton-Kraihanzel method have been correlated with Hammett, Taft and Swain-Lupton parameters.

Reactivity and selectivity, an intersecting-state view

A recently developed intersecting-state model which estimates energy barriers of chemical reactions in terms of thermodynamic, geometric, and electronic factors is employed to discuss the validity of several reactivity relations, namely the postulates of Hammond and Leffler, various linear free energy relationships, and the reactivity–selectivity principle. It is shown that such rules and principles are obeyed when all the changes in reactivity are dominated by changes in the reaction energy. The breakdown of such rules can occur when other factors such as the transition-state bond order, bond lengths, and force constants of the reactive bonds play a dominating role in chemical reactivity. Examples are provided to illustrate the practical limitations of the current reactivity–selectivity relations.

A theoretical study of the isotopic fractionation between gaseous and aqueous carbon dioxide

A computer simulation of 13 C and 18 O isotopic fractionations between gaseous carbon dioxide and its water solution has been performed. Two water molecules are necessary to model a direct participation of water in the solvation process. Furthermore, small changes in force constants of C02 bonds are required to account for the participation of water as a medium.

Variations of the silicon network of amorphous silicon studied by Raman spectroscopy

The structure of the silicon network of ‘device quality’ a-Si:H films is studied by means of Raman spectroscopy. An increase in the substrate temperature results in shift of the TO peak in the Raman spectra toward a high wavenumber and an increase in the compressive mechanical stress. A quasi-interstitial hydrogen model is proposed for the silicon network of a-Si:H. The model suggests that the shift of the TO peak in the Raman spectra originates from the change in the force constant of SiSi bonds induced by hydrogen atoms in a monohydride configuration.

Vibrational spectrum and force constants of xenon (II) fluoride

The vibrational Raman spectra of xenon (II) fluoride in the solid state and in the vapour at 325 K are reported. From the most precise wavenumbers of ν 2 and ν 3 from the infrared spectrum, and ν 1 from the Raman spectrum, the force constants of bond stretching, bond deformation and stretch—stretch interaction are evaluated using a SVFF approximation. From the solid state Raman spectrum the E g lattice vibration is assigned to the band at 111 cm −1.

Relativistic effects in molecules: pseudopotential calculations for TIH+, TIH and TIH3

Nonrelativistic, relativistic and semiempirical pseudopotentials have been used for investigating the effects of relativity and correlation on molecular properties (bond lengths, dissociation energies, force constants, multipole moments and ionization energies) of TIH+, TIH and TIH3. Spin-orbit effects are taken into account by using a quasirelativistic two-component pseudopotential. The influence of the core-valence correlation is accounted for by a core-polarization potential. Results obtained with the semiempirical pseudopotentials are in good agreement with experiment.

Vibrational force fields for strained hydrocarbons involving exo-double bonds. An ab initio study

Ab initio calculations of stretching force constants for the carbon-carbon double bond in a series of molecules characterized by different amounts of strain in the neighbourhood of the double bond were performed. The stretching force constants for bonds adjacent to the double bond have also been calculated as well as all relevant coupling terms. The variation in the force constant for the double bond is in agreement with the variations in bond distance predicted previously. Furthermore, it appears that the stretching force constants are linearly related to the product of s-character of the hybrids forming the bond in question, if other effects remain roughly constant. This seems to be the case in a series of studied molecules. It turns out that the strength of an exo-double bond is proportional to the amount of the angular strain inherent in the ring fragments attached to the double bond.

Diffraction Studies of a Highly Metastable Form of Amorphous Silica

An amorphous powder of SiO2 that calorimetric studies indicated to be energetically metastable by 46.9 ± 0.8 kj/mol relative to fused silica was studied by X‐ray diffraction. A calculation of the energetic instability, based on the bond length and bond angle distributions derived from the diffraction data and utilizing the force constants for bond stretching and bending, indicated that 41.3 ± 7.9 kj/mol of the instability may be associated with distortions of the Si‐O bonds, the O‐Si‐O bond angles, and the Si‐O‐Si angles. Analyses of the extensive small‐angle scattering from the porous material suggested that only a small portion of the instability is associated with surface structures.