Bond Force Constants Research Articles

Surface phonons of LaB 6(100): deformation of boron octahedra at the surface

The surface phonon dispersion of clean LaB 6(100) surface has been measured by means of high resolution electron energy loss spectroscopy. Eight vibrational modes, of which most are located in the energy gaps between the bulk phonon bands, have been detected. The lattice dynamical calculation of a slab-shaped crystal based on a force constant model has reproduced these experimental dispersion curves, which indicates the large increase in the force constant of interoctahedral boron-boron bond at the surface by 25%, and the large decrease in the force constants of intraoctahedral boron-boron bonds at the surface by 25–50%. These changes together with the analysis of the bulk phonon structure of metal hexaborides strongly suggest that the boron octahedra at the surface are expanded by about 0.004 nm parallel to the surface.

Infrared spectra of new dioxouranium (VI) solid complexes with tridentate schiff bases [UO 2(sal-OAP)(L)] (L = H 2O, Py, DMF and Et 3N)

The new dioxouranhun (VI) Schiff base complexes [UO 2sal-OAP)H 2O)], [UO 2(sal-OAP)(py)], [UO 2(sal-OAP)(DMF)] and [UO 2(sal-OAP)(Et 3N)](sal-OAP = orthoaminophenolsalicylideneiminato) have been prepared, and their i.r. spectra recorded and assigned on the basis of C s, symmetry. The bond stretching force constants of the uranyl bonds, F u = 0, were calculated as 661.7 Nm −1, 676.1 Nm −1, 674.5 Nm −1 and 674.5 Nm −1 for [UO 2sal-OAP)(H 2O)], [UO 2sal-OAP)(DMF)], [UO 2(sal-OAP)(py)] and [UO 2(sal-OAP)(Et 3N)], respectively. The corresponding values of the U = O bond lengths were calculated to be 1.745 Å, 1.741 Å, 1.742 Å and 1.742 Å.

Vibrational spectra of cyclopropenes. II. IR spectra of 1,2-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for the 1,2-dimethyl-3-phenylcyclopropene (I) and 1,2-diphenylcyclopropene (II) molecules. The forms of the normal vibrations were determined, and the vibrations associated with vibrations of the exo- and endocyclic bonds of the ring were distinguished. It was shown that substitution at the double bond of cyclopropene leads to a change in the form of the symmetrical vibration of the ring in comparison with the vibration of unsubstituted cyclopropene. It was shown that a significant hypsochromic shift of the band of the symmetrical ring vibration in 1,2-disubstituted cyclopropenes in comparison with cyclopropenes that do not contain substituents at the C1,2 atoms is due chiefly to the kinematic effect of the substituent. It was found that the introduction of substituents at the double bond of the ring leads to a decrease in the force constant of the double bonds.

Synthesis and Spectroscopic Studies of NN-O-Phenylenebis (Salicylideneiminato) Dioxouranium (VI) Solvates (L) CL = DMF and PY)

Abstract The two new complexes [UO2 (sal-o-phdn) (DMF)] and [UO2 (sol-o-phdn) (py)] (sal-o-phdn = N′-o-phenylenebis (salicylideneiminato) have been synthesized and their infrared and electronic spectra have been obtained and assigned beside those of the related complex [UO2 (sal -o-phdn)(EtOH)]. The values of both the bond stretching force constant of the uranyl bond, FU=O′ and U = O bond length have been calculated for each complex. The structure and geometry for each of the newlv prepared DMF and py complexes are discussed and compared with those known for the EtOH complex.

Lattice dynamics of the superconductor YBa2Cu3O7

AbstractA lattice dynamical formalism using the rigid ion model is applied to the superconductor YBa2Cu3O7. The model includes the short‐range repulsive interactions of axially symmetric type and long‐range Coulomb interactions among ion pairs. In order to determine the short‐range parameters, the Born‐Mayer approximation and the stability conditions were used. The crystal parameters determined by neutron powder diffration technique and the frequencies from Raman and infrared measurements on single crystal have been utilized to obtain the best fit. The proposed model yields an excellent agreement between the observed and calculated frequencies and gives all phonon modes of YBa2Cu3O7, which can serve as a guide for further experimental and theoretical investigations on YBa2Cu3O7 and other XnBa2Cu3O7 with similar structure. The realistic values of calculated effective charges and bond force constants and the agreement between the observed and calculated frequencies indicate the suitability of the rigid ion model with the proposed approximations to such materials. On the basis of our results, it is found that the atoms Ba and Cu(1) are strongly bonded to out‐of‐plane oxygen atoms. From the eigenvector analysis it appears as if the in‐plane oxygen atoms vibrate alone against the cage lattice with nearly half the frequency for x‐ and y‐directions in comparison to the z‐direction motion. This may have significance in connection with superconducting phenomena below Tc.

Nonlocal-density-functional bond-energy calculations of cage-shaped carbon fullerenes: C32 and C60.

The bond energies of ${\mathrm{C}}_{32}$ and ${\mathrm{C}}_{60}$ fullerenes have been calculated by a self-consistent molecular-orbital method based on nonlocal-density-functional theory with the generalized gradient approximation (GGA). These results were compared with those obtained with use of the local-density approximation (LDA). The bond energies calculated with the GGA (${\mathrm{C}}_{60}$, 7.24 eV/atom; ${\mathrm{C}}_{32}$, 6.88 eV/atom) were about 1.3 eV/atom (15%) smaller than those calculated with the LDA, and the GGA result for ${\mathrm{C}}_{60}$ was found to be in good agreement with the evaluated value from the experimental formation energy. The differences in bond lengths, force constants, and orbital energies for the same molecular structure ---except for the core orbitals---between the LDA and GGA were small, compared with the difference in bond energies.

Molecular mechanics calculations of transition metal complexes

A molecular mechanics force field appropriate for the modeling of Cu(II), Ni(II) (S = 1), Co(III), Fe(III), Cr(III), Zn(II), and Rh(III) complexes with amine, carboxylate, pyridine, and thia ether ligands is presented in its entirety. The parameters comprising the force field were determined by matching a large number of strain-minimized structures with their corresponding crystal structures. Within the force field, the only parameters that were altered from one system to another were the strain-free bond length and the force constant of the metal-ligand bond. The calculations indicate that some corrections for electronic effects have to be applied in order to obtain a consistent force field.

Interface vibrational mode in CdSe/ZnTe superlattices.

We have observed an interface vibrational mode in CdSe/ZnTe superlattices (SL's) by Raman scattering. The frequency of this interface mode lies above the optical-phonon bands of bulk CdSe and ZnTe compounds, and the ion displacements in the mode are sharply localized at the Zn-Se interfaces of the SL's. When the force constants of all four kinds of bonds in the SL's are taken to have the same values as in the corresponding bulk compounds, the frequency of this interface mode, 222 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, calculated using the linear-chain model is consistent with the experimental results, 222 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Both the smaller masses and the larger force constants of the interface bonds in the SL's rather than the mass effect alone, suggested previously, favor the appearance of the interface modes.

Thermodynamic properties of linear carbon chain molecules with conjugated triple bonds Part 2. Free radicals C nH ( n = 2–12) and C nN ( n = 2–11)

Reported values of rotational constants, vibrational fundamentals, excited electronic state energies, enthalpies of formation for C n ( n = 2–12) and C n N ( n = 2–11) radicals are reviewed and the recommended values selected. Molecular constants and enthalpies of formation for most of the radicals, which are known as the components of the interstellar gas or that are candidates for discovery in interstellar space, are estimated because the experimental data are not available. The similarity transference procedure is developed for the calculation of bond distances and force constants. Based on the selected values of molecular constants, the ideal gas thermodynamic functions for 21 radicals are calculated by the standard statistical mechanical method using rigid-rotor and harmonic-oscillator approximations. The calculated values of heat capacities C o p, Gibbs energies −( G o − H o 0)/ T, and enthalpies H o − H o 0, are fitted to the polynomial functions. The constants of these polynomials allow the values of C o p, − ( G o − H o 0)/ T and H o − H o 0 for considered radicals between 298.15 and 2000 K to be calculated. These constants together with the values of enthalpy of formation Δ H o (298.15 K), predicted using the estimates of bond dissociation energies are presented in this paper.

Vibrational and electronic spectra of matrix-isolated para-dichlorobenzene radical cations

A new pulsed-glow discharge technique has been used to generate the radical cations of para-dichlorobenzene (PDCB) and trap them in an argon matrix at 12 K. Three visible absorption bands with origins at 520.5, 490.6, and 322.4 nm are shown to be consistent with gas-phase photoelectron results and intermediate neglect of differential overlap/spectroscopy calculations. Resonance Raman and fluorescence spectra compare well with previous gas-phase electron impact excited emission and freon matrix (77 K) studies. The infrared spectrum of the PDCB cation has been measured for the first time and shows bands at 843, 986, 1110, and 1429 cm−1, all of which correlate well, in intensity, with the 520 nm electronic band. Ab initio self-consistent-field level calculations on the PDCB neutral and radical cation species reproduce the spectra well, after scaling is performed. It is shown that, upon ionization, the C–Cl bond force constants and the ring central C–C bond force constants increase, while the force constants for the ring C–C bonds adjacent to the C–Cl bond decrease. This accounts for the observed blue shift for certain bands and the red shift for certain others when PDCB is ionized.

An unusual relationship between the nitrogen-fluorine bond lengths and force constants in N-fluoroamines

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn unusual relationship between the nitrogen-fluorine bond lengths and force constants in N-fluoroaminesDines Christen, Om Dutt Gupta, Johannes Kadel, Robert L. Kirchmeier, Hans Georg Mack, Heinz Oberhammer, and Jeanne M. ShreeveCite this: J. Am. Chem. Soc. 1991, 113, 24, 9131–9135Publication Date (Print):November 1, 1991Publication History Published online1 May 2002Published inissue 1 November 1991https://doi.org/10.1021/ja00024a016RIGHTS & PERMISSIONSArticle Views295Altmetric-Citations32LEARN 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 (559 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The bulk modulus of C60 molecules and crystals: A molecular mechanics approach

In this letter, the bulk modulus of an individual C60 molecule is calculated in terms of the C,C bond force constant. A range of values for the bulk modulus is obtained with literature values for the force constant. The values obtained all exceed the bulk modulus (441 GPa) of diamond. With a C,C bond force constant equal to that between adjacent carbon atoms in graphite, 7.08 mdyn/Å, a bulk modulus of 903 GPa is obtained. On the basis of a simple composite model it is calculated that single closest-packed C60 crystals of C60 will have a bulk modulus of roughly 668 GPa under hydrostatic pressures. The calculated bulk modulus for a single C60 ‘‘buckyball’’ therefore suggests the possibility that a C60 crystal could be the most incompressible material known, at a pressure above about 50 GPa.

Study of alkali metal adsorption on reconstructed and unreconstructed Cu surfaces by HREELS

The study of the stretching mode of Li, Na and K on various Cu surfaces show that the force constant of the adsorbate-surface bond depends neither on coverage nor substantially on the particular type of alkali atom. On the Cu(110) surface the spectra also infer that the (1 × 2) reconstruction may be induced by a local coverage less than 0.03 monolayers.

Schwingungsspektren und Normalkoordinatenanalyse der heteroleptischen Halogenohexaborate B6XnY6-n 2-, n = 1-5; Χ ≠ Υ = Cl, Br, I / Vibrational Spectra and Normal Coordinate Analysis of the Heteroleptic Halogenohexaborates B6XnY6-n 2-, n = 1— 5; Χ ≠ Y = Cl, Br, I

Normal coordinate analyses for the 24 mixed halogenohexaborates B6XnY6-n 2-, n = 1—5, Χ ≠ Y = Cl, Br, I, including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. Using the bond lengths and force constants for the homoleptic species B6X6 2-, which with respect to the B6 cage are weighted standardized, the calculated frequencies are in good agreement with observed IR and Raman bands. The boronhalogen stretching vibrations for symmetric molecular axes correspond with the Ra(IR) bands of the homoleptic compounds: ClB6Cl 327 (515), BrB6Br 207 (430), IB6I 152 (394) cm-1. As a characteristic feature the mixed halogeno clusters exhibit bands with nearly averaged frequencies from asymmetrical axes: ClB6Br 261 (487), ClB6I 227 (473), BrB6I 178 (409) cm-1. This complete vibrational coupling is confirmed by properly balanced potential energy distribution on BX and BY bonds. There is a slight influence of the different substituents on the internal modes of the B6 cage (pseudo-Oh), observed in the sequence A1g>T1u> Eg>T2g in the region 1220-740 cm-1. The bands are shifted about 100 cm-1 with increasing mass of halogen, broadened by boron isotopomers (max. 60 cm-1), and degenerate vibrations are split by lowered point and site symmetry up to 100 cm-1.

Thermodynamic properties of linear carbon chain molecules with conjugated triple bonds: Part I. Polyacetylenes, H(CC) nH ( n = 2–6), cyanopolyacetylenes, H(CC) nCN ( n = 1–5), and dicyanopolyacetylenes, NC(CC) nCN ( n = 1–4)

The available structural parameters, fundamental frequencies and enthalpies of formation, if any, for polyacetylenes, C 2 n H 2 ( n = 2–6), cyanopolyacetylenes, HC 2 n+1 N ( n = 1–5), and dicyanopolyacetylenes, C 2 n N 2 ( n = 2–5), which are known to be interstellar molecules, were critically evaluated and the recommended values selected. Molecular constants and enthalpies of formation for most of the molecules were estimated as the experimental values for these compounds are not available. The similarity transference procedure has been developed for the calculation of bond distances and force constants. Using a rigid-rotor and harmonic-oscillator approximation, this information was utilized to calculate the ideal gas thermodynamic functions for 14 molecules. The calculated values of heat capacities, C p°, Gibbs energies, -( G°- H 0°)/ T, and enthalpies, H°- H 0°), were fitted to the suitable polynomial functions. The constants of these polynomials allow the values of C p°, -( G°- H 0°)/ T) and H°- H 0°)/ T for considered compounds between 298.15 and 2000 K to be calculated. These constants together with the values of enthalpy of formation, Δ f H° (298.15 K), estimated using the group additivity method are presented in the paper.

Lattice-dynamical model of crystalline DNA: Intermolecular bonds and the A to B transition.

A lattice-dynamical model has been developed of DNA in a crystalline lattice. This model is used to evaluate the harmonic nearest-neighbor force constants of highly oriented films of Na-, K-, Rb-, and Cs-DNA as a function of relative humidity from Raman data. These DNA-counterion systems were chosen since they all undergo an A to B transition. The analysis suggests that the A to B transition takes place in these different DNA's when the effective force constant of the intermolecular bond falls below a ``critical'' value.

Transferability of the electronic structure characteristics of saturated molecules

AbstractThe common quantum mechanical problem for the total class of saturated hydrocarbons has been stated and solved within the framework of the effective Hamiltonian method. A quantum mechanical substantiation of the transferability of the electronic structure characteristics (bond dipole moments, bond energies, and bond force constants) as well as the investigation of the origin of transferability have been considered for the stated class of chemical compounds.

Direct study of unstable dimethylgermathione, Me 2GeS, by vacuum pyrolysis-MS and low temperature matrix IR spectroscopy

Dimethylgermathione, Me 2GeS (D 1), has been studied by vacuum pyrolysis-MS and matrix isolation IR spectroscopy. The germathione D 1 was generated in the gas phase by pyrolytic decomposition (730–900°C, 10 −2 −10 −3 Torr) of the trimer (Me 2GeS) 3 (D 3) in a quartz pyrolyzer, coupled to the ionization chamber of mass spectrometer or to an optical helium cryostat, where pyrolysis products have been frozen at 12 K in an argon matrix. The ionization energies (IE) of D 3, D 1 and its cyclodimer (D 2) have been determined from measurements of ionization efficiency curves in mass spectra of pyrolysis products of D 3 and using the semilogplot tehcnique. The IE revealed for D 1 (8.63±0.1 eV) practically coincided with that obtained earlier by PES, which proved the formation of monomeric D 1 in the reaction. In the matrix IR spectra (Ar, 12 K) of pyrolysis products of D 3 the bands 518, 574, 606, 765, 809, 850, 1231 and 1392 cm −1, disappearing simultaneously inw arming-up experimnts (to 35–40 K). These were ascribed to germathione D 1. By comparison of experimental frequencies with the calculated values the band 518 cm −1 was assigned to GeS stretching vibration. The calculated geS bond force constant (4.08 mdyn/Å) is a direct physical characteristic, giving strong evidence for considerable duoble bonding in dimethylgermathione.

Phonon Interaction Free Energy Between Adatom and Impurity11 The project supported in part by NSERC of Canada.

The change of the phonon contribution to the free energy, , due to the interaction between an adatom and an impurity substrate atom is calculated by expressing as a contour integral in the complex-frequency plane and evaluating it directly along a suitably chosen contour numerically. Results are given as a function of the adatom-surface bond force constant, the mass defect of the impurity atom, and the adatom-impurity separation for both a one-dimensional and a three-dimensional simple cubic model substrate.

The harmonic force field and rz molecular structure of disulphur monoxide, S 2O

The harmonic force field for S 2O has been determined from a least-squares refinement to an extensive data set, which included vibrational wavenumbers, isotopic shifts and centrifugal distortion constants. Principal force constants are k R (SS) = 4.610 (39) aJ Å −2, k r(SO) = 8.583(70) aJ Å −2 and k α(SSO) = 1.326(6) aJ rad −2. The value of ν 3 measured in an inert gas matrix appears incompatible with the remaining gas-phase data. Standard ab initio DZ (P)/SCF calculations predict the molecular structure of S 2O quite satisfactorily, but their predictions concerning the force field are of uneven quality, especially for the off-diagonal elements. The r z molecular structure S 2O has been obtained, and is compared with the r 0, r s and r e representations. Bond lengths and force constants for related sulphur-containing molecules are compared, and correlations with the apparent participation of d orbitals on sulphur are discussed.