Lattice oligomer dynamics

Exact results are obtained for the dynamics of short chains on the cubic lattice in the presence of excluded volume. The dynamics is used to evaluate the vector end-to-end length and squared length correlation functions. These functions are compared to those obtained by computer simulation by Kranbuehl and Verdier for longer chains. A coherent picture of the effects of excluded volume and chain length on the system properties sampled is found.     

Lattice dynamics of cuprous iodide

The lattice dynamics of cuprous iodide have been investigated on the basis of an ‘11-parameter’ rigid-ion model (RIM). The reported neutron scattering data of CuI are reasonably well decribed by the model, especially when an optimized procedure for the selection of parameters is used. Results are presented for the phonon dispersion curves of CuI. The critical point phonon (CPP) frequencies inferred from the model are shown to provide satisfactory assignments of the observed two-phonon features in the available Raman spectrum.     

Lattice dynamics of single-bonded cubic nitrogen

The first principle calculations of the lattice dynamical properties of the single-bonded cubic nitrogen were performed using the density-functional perturbation theory together with plane-wave expansion and nonlocal pseudopotentials. The equilibrium structure of the single-bonded cubic nitrogen was first evaluated via the minimization of the total energy. Then, the harmonic phonon dispersion curves and the density of phonon states of the single-bonded cubic nitrogen have been evaluated within the linear-response framework. Furthermore, the heat capacity, enthalpy, free energy, entropy and velocity of sound of the single-bonded cubic nitrogen were calculated.     

Lattice dynamics of solid hydrogen chloride

Lattice dynamics of solid hydrogen chloride is studied, assuming a rigid molecule, in the harmonic and pair potential (Lennard-Jones interaction) approximation between atoms with the inclusion of electrostatic interactions between point dipoles placed on atomic centres. The potential parameters for each of the different non-bonded atom pairs were obtained by means of an optimization routine to give a least-squares fit to observed zone centre (k = 0) frequencies, equilibrium conditions and lattice energy of the lattice.     

Lattice dynamics of solid α-carbon monoxide

The lattice dynamics of α-CO is studied assuming a fully-ordered antiferro P2₁3 structure, using a potential model which includes electrostatic, dispersion and exchange interactions. The coupling of translational and librational motions leads to mixed modes at finite wave vectors and to anomalous acoustic dispersion. Anharmonic frequency shifts and the damping due to phonon—phonon interactions are evaluated for the zero wave vector modes. The single-particle potential wells for the high-frequency librational modes are investigated and suggest that translation—rotation coupling plays a primary role in the molecular reorientations.     

Lattice dynamics of InAs under hydrostatic pressures

The lattice dynamics of InAs under variable hydrostatic pressures is investigated on the basis of an ‘11-parameter’ rigid-ion model (RIM). The calculated phonon dispersion curves are in satisfactory agreement with the neutron scattering data (available for the TA modes only) measured at room temperature and atmospheric pressure. The one- and two-phonon densities of states functions and mode Gruneisen parameters have been computed at two arbitrary hydrostatic pressures. The effect of high pressure on the phonon dispersion curves is shown to lead to a typical ‘softening’ in the transverse acoustic modes and eventually to a phase trnasformation of the compound.     

Thiobenzophenone and tetracyanoethylene

The title reaction furnished the yellow 3,4-dicyano-2,5-bis(diphenylmethyleneamino)-thiophene and a red precursor which contains one more sulfur atom; structures and mechanism are discussed.     

Lattice dynamics and interaction potentials in molecular crystals

This paper, based essentially on the work done in recent years in our laboratory, presents a critical analysis of harmonic and anharmonic calculations of crystal vibrations in the determination of intermolecular potentials. The main purpose is to show that the dynamical properties are specifically sensitive to different terms of the potential and thus that information extracted from vibrational spectra of crystals is of the greatest importance for the theory of intermolecular forces. The most important conclusion is that these calculations point to the development of anisotropic short-range potentials and orient future researches towards the more complex and elaborate anharmonic treatment of crystal vibrations.     

Lattice dynamics of carbon chain inside a carbon nanotube

Based on the density functional theory, we obtain the optimum geometry of carbon chain inside a carbon nanotube. The phonon spectrum and specific heat of such a chain and nanotube hybrid system are calculated in terms of lattice dynamics theory. Some new phonon branches that have been obtained come from the coupling vibrations of the nanotube and the chain. The bending and stretching modes of the chain appear at about 520 cm(-1)and 1935 cm(-1) at Gamma point, respectively. It is found that the softening of G modes results mainly from the chain induced variations in the bond length on nanotube, independent of van der Waals interaction, while the stiffening of radial breathing mode is developed by the competition between the two factors. In the low-frequency region, the vibrational density of states are very different from that of the bare nanotube. Its specific heat implies the underlying quantized phonon structures and much large thermal conductivity in the hybrid system. In addition, the chain-length dependent vibration modes are calculated, from which it is expected that a finite chain of about 14 carbon atoms in the nanotube may produce the experimental Raman peak at about 1850 cm(-1).     

Reactions of primary amines with tetracyanoethylene

Primary amines, 3-triethoxysilylpropylamine, 3-silatranylpropylamine, and cyclohexylamine, react with tetracyanoethylene in acetonitrile at room temperature via addition at the cyano group to afford the corresponding amidines. N-Cyclohexyltricyanoacrylamidine exists as a mixture of two of the three possible isomers, while N-(3-triethoxysilylpropyl)tricyanoacrylamidine and N-(3-silatranylpropyl)tricyanoacrylamidine exist mainly as a single isomer containing NH₂ group. N-(3-Triethoxysilylpropyl)tricyanoacrylamidine was used to prepare gels and films.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 9, 2004, pp. 1308–1314.Original Russian Text Copyright © 2004 by Ladilina, Semenov, Kurskii, Khorshev, Domrachev.     

Metal-acetylide addition to tetracyanoethylene

Two push-pull chromophores that have shown utility in the field of molecular electronics and non-linear optics are DDMEBT (1, 2-(4-dimethylamino)phenyl)-3-((4-(dimethylamino)phenyl)ethynyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile) and TDMEE (2, 4-(4-dimethylamino)phenyl)but-1-en-3-yne-1,1,2-tricarbonitrile). Unfortunately, the methods reported for their synthesis give variable yields, use toxic solvents, and only provide small amounts of material. We report improved synthetic protocols, providing access to larger quantities of material. By investigating multiple metal-acetylides of 4-ethynyl-N,N-dimethylaniline and their subsequent addition to TCNE, we obtained various products depending on the identity of the metal ion. This led to the simple synthesis of push-pull chromophoric compounds.     

Lattice theory of ultrafast excitonic and charge-transfer dynamics in DNA

We propose a lattice fermion model suitable for studying the ultrafast photoexcitation dynamics of ordered chains of deoxyribonucleic acid (DNA) polymers. The model includes both parallel (intrachain) and perpendicular (cross-chain) terms as well as diagonal cross-chain terms coupling neighboring bases. The general form of our Hamiltonian is borrowed from lattice fermion models of quantum chromodynamics. The band structure for this model can be determined analytically, and we use this as a basis for computing the singly excited states of the poly(dA)poly(dT) DNA duplex using configuration interaction singles. Parameters for the model are taken from various literature sources and our own ab initio calculations. Results indicate that the excited states consist of a low energy band of dark charge-separated states followed by separate bands of delocalized excitonic states which have weak mixing between the thymidine and adenosine sides of the DNA chain. We then propose a lattice exciton model based upon the transition dipole-dipole couplings between bases and compare the analytical results for the survival probability of an initially localized exciton to exact numerical results. The results herein underscore the competing role of excitonic and charge-transfer dynamics in these systems.     

Molecular associations between indolizines and tetracyanoethylene

Spectroscopic, thermodynamic and kinetic properties of molecular interactions between indolizines and tetracyanoethylene are reported. The interactions involved in the complexes are weak as evidenced by the low formation constants. The kinetic behaviour indicates the initial formation of a pI-complex that is rapidly transformed into a σ-complex and thereafter into the final adduct(s). Apart from the results obtained by other techniques, infrared data clearly evidence vibrational contributes characteristic of the complexes, the tricyanovinyl derivatives and the tetracyanoethylene radical anion.     

Lattice dynamics with second-neighbor interactions. III. Green's matrix

The theory of pth-order singular differential equations is adaptable to the study of the system of recurrence relations occurring in the problem of a one-dimensional chain with pth-neighbor interactions. By using Green's formula, a mapping is defined between the space V_n of eigenvectors to the dynamical matrix and the symplectic space V_2p of boundary conditions for the recurrence equations. The properties of the resolvent are obtained from an analysis of the solutions of a system of inhomogeneous equations and Green's matrix is constructed for the case of standard Sturm–Liouvilletype boundary conditions. The Weyl surface is discussed and its properties used for the construction of square summable sequences which in turn can be employed in expansion formulas. The generalization of Weyl's m-function in the second-order case (p = 1) becomes for p ≥ 2 a p × p matrix M (λ), where λ is a complex parameter. The imaginary part Im { M (λ)} is related to the spectral properties and serves as basis for the discussion of different concepts of spectral density for the normal modes of lattice dynamical problems. An important practical result is the equation M = ?ΨΦ_a valid in the limit point case, generalizing the corresponding second-order formula.     

Lattice dynamics of the high-pressure monoclinic phase of solid carbon tetrachloride

Two intermolecular potential functions (models I and II), recently proposed for liquid CCI₄, are used to study the lattice dynamics of the monoclinic high-pressure solid, phase III. Model II agrees reasonably well with the measured Raman Spectrum.