Finite-size dimensional analysis of the superconducting vibronic interaction

Even in a finite-size system, the vibronic interaction acts as the attractive force to bind a pair of electrons. For small-size systems, the electron repulsion overwhelms the vibronic attraction. As the size of the system becomes large, the electronic repulsion diminishes to zero in proportion to the volume of the system, whereas the vibronic attraction (1) grows to infinity for a one-dimensional system, (2) converges to a finite value for a two-dimensional system, and (3) diminishes to zero for a three-dimensional system. Even for a three-dimensional system, the vibronic attraction diminishes much slower than does the electronic repulsion. This brings about a concept of the critical size for an any-dimensional system, over which size the vibronic attraction overwhelms the electronic repulsion, thereby creating purely attractive interaction for a pair of electrons, which may lead to superconductivity.     

On quantifying the vibronic interaction between electronic states

An accurate estimation of the interstate vibronic coupling strength is of particular relevance for the treatment of nonadiabatic dynamics. This is not a trivial task because direct interactions between electronic states have to be separated from intrinsic frequency shifts. Surprisingly, this issue has not been discussed in detail in the literature so far. An analysis of the error dependence is given for two formulas derived from linear vibronic coupling theory. The difficulty in estimating the interstate coupling parameters is shown to originate from the initially unknown contribution of the diagonal quadratic coupling coefficients to the total vibronic coupling. An interpretation of the error analysis including a numerical case study is followed by a more general discussion of the different mechanisms that can shape adiabatic electronic potential energy functions. Qualitative criteria are formulated for the differentiation between interstate and intrastate vibronic coupling effects based on electronic structure information. These ideas are then applied to investigate vibronic coupling problems in pyrazine as well as trans- and cis-hexatriene.     

Polymer-induced depletion interaction between weakly attractive plates

Lattice Monte Carlo simulations have been employed to calculate depletion interaction of excluded volume chains in a weakly attractive slit, particularly in the region around the critical point of adsorption. The simulations were performed under full equilibrium conditions where a dilute solution in a slit was in contact with the reservoir. The free energy of confinement deltaA, the force f, and the relative pressurepI/pE on the slit walls were calculated as a function of slit width D and the attraction strength epsilon. The depletion region in the pressure profile pI/pE vs D is reduced by an increase in the attraction potential epsilon in a manner resembling the influence of polymer concentration. At the critical point of adsorption epsilonc the depletion interaction vanishes both in the pressure pI/pE and in the intraslit concentration profile phiI(x). The parameters used to assess the stability of colloidal dispersions such as the depletion potential W(D) (an integral of the net pressure deltap) reach a unique value at the critical condition. A monotonic repulsive profilepI vs D was found for chains trapped in the slit at restricted equilibrium. The mean dimensions (R2) of chains compressed in attractive slits feature a distinct minimum at intermediate slit widths.     

A new algorithm for the variational solution of the vibronic problem for polyatomic molecules

A new effective algorithm for solving the complete vibronic problem by the variational method is proposed. The algorithm reduces the variational matrix by successively including the shift and entanglement of normal coordinates and using recurrent formulas for determining the eigenvectors of the matrix. No additional approximations are used. The method is faster than those used previously by two or more orders of magnitude. This work was supported by the Russian Fundamental Research Fund (93-02-3405). K. A. Timiryazev Moscow Agricultural Academy. Translated fromZhurmal Strukturnoi Khimii, Vol. 35, No. 6, pp. 23–30, November–December, 1994. Translated by O. Kharlamova     

A vibronic model for exchange-coupled mixed-valence dimers

A quantum-mechanical calculation of the spin—vibronic states of an exchange-coupled mixed-valence dimer is presented. It is shown that the temperatur     

Gelation of native beta-lactoglobulin induced by electrostatic attractive interaction with xanthan gum

The mechanism and kinetics of the electrostatic gelation of native beta-lactoglobulin-xanthan gum mixtures in aqueous solution is reported. The total biopolymer concentration at which gelation was obtained was extremely low (0.1 wt %) compared to the usually tested concentrations for protein-polysaccharide mixed gels (4-12 wt %). This is, to our knowledge, the first time that oppositely charged proteins and polysaccharides are reported to form a gel without applying any treatment to denature the protein (e.g. heating, enzymatic hydrolysis) and at such low concentrations. Static light-scattering and viscoelastic measurements allowed determination of the gelation kinetics. It was found that the gelation process initiated following a similar path as that of an associative phase separation process, i.e., with the formation of primary and interpolymeric electrostatic complexes. However, interpolymeric complexes were able to form clusters and junction zones that resulted in the freeze-in of the whole structure at the point of gelation. The formed gel is therefore a coupled-gel, that is, a gel that has junction zones involving two different molecules. The structuration of xanthan gum, even at these low concentrations, may have played a role in the structuration process. Due to the electrostatic nature of the gels, there was an optimum pH and macromolecular ratio at which the stability of the gels was maximal. This was related to the existence of a stoichiometric electrical charge equivalence pH, where molecules carry equal but opposite charges and protein-polysaccharide interactions are at their maximum.     

On attractive interaction of a colloid pair of like charge at infinite dilution

Numerical data on the potential of mean force W(r) at infinite dilution of a highly charged colloid pair embedded in a 1:1 electrolyte are reported. The authors obtain attractive minima (W<0) at short interparticle distance in these potential functions in hypernetted chain (HNC) approximation, as salt concentration is increased. These minima, however, disappear in all system sets studied when a self-consistent Zerah-Hansen (ZH) closure is used. The authors infer that the attractive minima obtained in a HNC closure are spurious and result from the neglect of bridge diagrams in HNC approximation. An expression of bridge function, which the ZH closure in effect incorporates in W(r) to remove attractive minima, is derived in terms of modification of correlation functions. Features of repulsive pair potentials obtained using the ZH closure, their dependence on particle charge and salt concentration, and their agreement with those of the Derajguin-Landau-Verwey-Overbeek theory are investigated.     

On the floating basis set model for studying the vibronic interaction in polyatomic molecules

The floating basis set model by Johnson and Weigang is reinvestigated using a general picture of the molecular hamiltonian. It is found that Johnson and Weigang, though considering explicitly that electrons move with the nuclei, ignored a contribution to the electronic wavefunction from the coupling of the vibrational and electronic motions of the electrons. The vibrational wavefunctions and energies of the molecule are also modified.     

A new viscometric criterion for polymer-polymer interaction

Based on a simple cluster theory recently proposed for the viscosity of polymer dilute solution, a new viscometrical criterion was suggested to probe the interaction between unlike polymers. The new criterion was applied into some polymer mixture solutions to study the polymer-polymer interactions. It was found the new criterion is more reasonable.     

A new class of ion-ion interaction: Z-bond

The hydrogen-bond interactions in ionic liquids have been simply described by the conventional hydrogen-bond model of A–H···B. Coupling with the strong electrostatic force, however, hydrogen bond between the cation and anion shows particular features in the geometric, energetic, electronic, and dynamic aspects, which is inherently different from that of the conventional hydrogen bond. A general model could be expressed as +[A–H···B]-, in which A and B represent heavy atoms and + and – represent the charges of the cation containing A atom and anion containing B atom, respectively. Because the structure shows a zig-zag motif, this coupling interaction is defined here as the Z-bond. The new model could be generally used to describe the interactions in ionic liquids, as well as bio-systems involved in ions, ionic reaction, and ionic materials.     

A strategic approach for the synthesis of new porphyrin rings, attractive for heme model purpose

Novel complexes have been efficiently synthesized with a facile route using two different atropisomers of the same porphyrin. These compounds feature a tridentate binding site, a tyrosine molecule, and a proximal base, all bound to the porphyrin ring in different fashions, making them attractive for heme modeling purposes.     

A new interpretation of the Baylis-Hillman mechanism

[reaction: see text] On the basis of reaction rate data, we have proposed a new mechanism for the Baylis-Hillman reaction involving the formation of a hemiacetal intermediate. We have determined that the rate-determining step is second order in aldehyde and first order in DABCO and acrylate. We have shown that this mechanism is general to aryl aldehydes under polar, nonpolar, and protic conditions using both rate data and two isotope effect experiments.     

Effects of the vibronic interaction on anisotropy of ESR parameters for three-coordinate complexes of univalent nickel

Vibronic interaction effects on anisotropy of ESR parameters for three-coordinate complexes of univalent nickel have been investigated. Analytical expressions in the first order of the perturbation theory were obtained for wave functions of the ground and excited doubly degenerate states having taken into account vibronic and spin-orbital interactions. Based on the assumption that the vibronic interaction prevails over spin-orbital, there were obtained the expressions for main components of the g-tensor and isotropic HFS constants with ligand cores which are consistent with experimental data for three-coordinate complexes of the composition [Ni(PPh₃)₃]BF₄ and [Ni(PCy₃)₃]BF₄.     

Some comments on vibronic intensities of naphthalene fluorescence spectra from single vibronic levels

It is shown that some features of intensity distribution among certain vibronic transitions in naphthalene molecule can be understood, when one takes into account adiabatic and nonadiabatic interaction between S₁(¹B_3u), S₂(^tB_2u), and S₃(^IB_3u) electronic states. the vibronic activity of the $\text{6}\text{?}$(b_1g) mode in naphthalene-d₈ can be explained in terms of an anharmonic coupling with the $\text{7}\text{?}$(b_1g) mode. The theoretical analysis suggests reinterpretation of some vibronic transitions.     

Intermolecular vibronic coupling and the mechanism of formation of hexatrienes from benzene in viscous media

The photochemistry of benzene and some of its alkyl derivatives has been studied in deuterated alcohol at 77°K. Intermolecular vibronic coupling of triplet benzene occurs with C-H but not O-H vibrational modes in the solvent. The coupling is sensitive to the relative orientation of the neighbouring molecules and in favourable cases, leads to the formation of a hexatriene in a concerted process.     

A rotation–torsion vibronic band contour program

A Fortran-77 computer program has been written which calculates the rotation–torsion profile of a vibronic transition using an asymmetric top/free internal rotor Hamiltonian. The program is applicable to any molecule that is composed of a frame portion of C_2v symmetry a free rotor portion of C_3v symmetry. Rotation–torsion bands of A-, B-, and C-type contours may be calculated within an assumed Boltzmann distribution of rotation–torsion level populations or within a specified non-Boltzmann distribution of torsional level populations.