Probability estimate for intersystem crossings in naphthalene and acenaphthene in the presence of benzophenone

To a first approximation in perturbation theory, we have obtained expressions for the rate constants for intersystem crossings in acceptor molecules. We show that exchange interactions between the components of the donor-acceptor pair can change the probability of intersystem crossings for both radiative T → S₀ and nonradiative S₁ → T transitions. The theoretical conclusions are supported by the results of experimental studies. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 550–553, July–August, 2006.     

Contribution of intersystem recombination on the lifetime of radical pair produced in photoreduction of benzophenone derivatives in SDS micelle as detected by pulse-PYESR

The heavy atom effect on the radical-pair lifetime was studied on the photochemical hydrogen-abstraction reaction of benzophenone and its derivatives having halogen atoms in the phenyl group in an SDS micellar solution by using the pulse-mode product-yield-detected ESR technique. Upon introducing bromine atoms in the benzophenone frame the lifetime was shortened considerably, though no appreciable effects were found for other systems with lighter halogens. Through estimation of the several factors which may affect the lifetime of radical pair upon the halogen introduction, we concluded that the intersystem recombination, which is the geminate recombination of redical pair from the triplet state, was the main mechanism of the observed shortening of the lifetime.     

Dynamic light scattering in solid polymers

The viscosity of an amorphous polymeric solid above its glass transition [T _g (T,P)] increases as the temperature of the solid is decreased or the pressure is increased. Under changes in temperature or pressure, molecular subunits in the polymeric solid undergo configurational changes. Such changes or relaxations have a distribution of relaxation strengths and times. As the solid is cooled or as the hydrostatic pressure on the solid is increased, the relaxation strengths increase and the relaxation times increase. These changes in relaxation or dynamic properties are very dramatic as the empirical T _g is approached. Near T _g the polymeric solid is no longer in volume equilibrium; continued cooling or pressuring at a time rate faster than the average relaxation time will produce a polymeric glass. This glass is a nonequilibrium, amorphous solid. If the glass is held at a fixed temperature and pressure very close to, but below, T _g , the volume of the glass will be observed to relax to its equilibrium value. For temperatures and pressures well below T _g , equilibrium is a much more conjectural concept since the relaxation times become extremely long. It has been proposed^1,2 that there is a characteristic temperature T _g at which an amorphous polymer undergoes a second-order transition to an equilibrium glass with zero configurational entropy (i.e., a noncrystallizable solid).     

Heat capacities of solid polymers

The heat capacity of a solid polymer is governed by the manner in which the internal energy is distributed over the various degrees of freedom. If the internal energy manifests itself in harmonic oscillatory motions, the heat capacity is the sum of contributions of the normal modes of motion. In practice, full frequency data are not generally available for polymers. This paper proposes an empirical method for determining the heat capacities of linear high polymers by the addition of contributions from different chain segments. A survey of heat capacity data for 30 linear high polymers and several copolymer systems has revealed that additivity is usually valid for a temperature range from about 60°K to the glass-transition temperature. A table of heat capacity contributions of a number of polymer constituents is derived which permits the calculation of unknown heat capacities to an accuracy of ±5% or better. In addition, δC_p data for the increase of the heat capacity at the glass-transition temperature were found to agree with the rule of constant heat capacity increase per mole of “bead” proposed 8 years ago.     

Spectral migration and decay characteristics of triplet excitations in glassy benzophenone

Spectral and kinetic properties of triplet excitons in thin films of glassy benzophenone were studied at temperatures between 4.2 and 220 K. The influence of the film thickness on the lifetime and nature of their phosphorescence decay was observed and discussed. It was shown that studies of spectral diffusion in thin glassy films of benzophenone must take into account the dependence of the emission lifetime on the recording wavelength and the influence of the excitation intensity on the phosphorescence decay process, among other factors. The hypothesis is put forward that the characteristics of the temperature transformations of the spectra (displacements, changes in band half-widths) are related to phase transitions and relaxation processes in the glassy benzophenone. Fiz. Tverd. Tela (St. Petersburg) 40, 1052–1055 (June 1998)     

Step deformation of solid amorphous polymers

The variation of step deformation kinetics in solids is studied as a function of morphological factors. Oscillations of creep rate at micrometer increments of the amount of deformation, which reflect the step nature of the process, are investigated from an interferogram. It is shown that the plasticization of polymethyl methacrylate by dibutyl phthalate blurs the steps, while their height varies insignificantly. The results are explained using the concept of the netlike structure of amorphous polymers. The data obtained confirm the universal nature of jumps as a mode of evolution of deformation in various solids. The jumps reflect the cooperative nature of motion of kinetic units, and the regular variation of the characteristics of the jumps lends support to the definition of creep as a process of structural self-organization.     

On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction

We examine the stability of the valence bond solid (VBS) phase against the Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. We consider the VBS states in the AKLT model as well as the one in the Sandvik model in the 4×L lattice. We found that the VBS is very stable against the DM interaction qin the AKLT model. There is no quantum phase transition in the AKLT+DM case. However, the VBS spin gap closes in the Sandvik model due to the DM interaction.     

Deformation of solid polymers in a constant magnetic field

The effect of a constant magnetic field on the creep rate is investigated for poly(vinyl butyral), styrene-methacrylic acid copolymer [poly(styrene) + 16 wt % methacrylic acid], poly(methylene oxide), and other polymers. It is demonstrated that the constant magnetic field can variously affect different polymers and that the effect of the magnetic field is enhanced in a particular range of strain rates.     

Singlet-singlet energy transfer in liquid solution between Rhodamine 6G and benzophenone in presence of non-linear absorption

Results are presented on non-linear absorption of benzophenone in a methanol solution. Using a mixture of Rhodamine 6G and benzophenone, we show the possibility of singlet-singlet energy transfer between these two molecules.The experimental data give a value for the energy transfer probability of 10¹² M^?1 sec^?1.     

Characterization of silver nanomeshes generated by laser-induced photoreduction from a solid silver nitrate thin film

This study characterizes electrical properties of silver thin films with meshed nanostructures fabricated through the photoreduction of solid silver nitrate thin films using excimer laser irradiation. Variations of mesh morphology as functions of laser irradiation time and fluences are examined; and the relationship between the film’s electrical resistance and mesh structure are addressed. The course of nanomesh formation can be separated into two main phases: precipitation of silver nanoparticles as a result of photoreduction; and, formation of mesh nanostructures through the photothermal effect. The resulting electrical resistance depends strongly on the mesh nanostructure. With a suitable arrangement of laser fluence and irradiation time, silver thin films with well interconnected nanomeshes can be fabricated. Results show that silver thin films with low electrical resistivity, down to 8.5×10⁻⁸ Ω m, are easily obtainable. The laser reduction approach takes advantage of the flexibility in local patterning. Moreover, the reduction is from a solid silver nitrate thin film and is executed in the ambient environment that renders this approach a potential method for low-temperature fabrication of metallic electrode conductors for organic electronics.     

Type-II intermittency characteristics in the presence of noise

We consider a type of intermittent behavior that occurs as the result of the interplay between dynamical mechanisms giving rise to type-II intermittency and random dynamics. We analytically deduce the law for the distribution of the laminar phases, which has never been obtained hitherto. The already known dependence of the mean length of the laminar phases on the criticality parameter [Phys. Rev. E 68, 036203 (2003)] follows as a corollary of the carried out research. We also prove that this dependence obtained earlier under the assumption of the fixed form of the reinjection probability does not depend on the relaminarization properties, and, correspondingly, the obtained expression of the mean length of the laminar phases on the criticality parameter remains correct for different types of the reinjection probability.     

Dynamical polarization of protons in some polymers using the solid effect method

Experimental results on the dynamical polarization of protons in various polymers irradiated by neutrons are recapitulated. The measurements were performed at liquid nitrogen temperatures. The dependence was investigated of the degree of polarization on the microwave power, on the irradiation dose and on the change in frequency of the nuclear magnetic resonance. The maximum enhancement of polarization was obtained for polyethylene of a density 0·95 g/cm³ and was equal to 30.

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SOLID EFFECT

. . , . , 30, 0,95 g/cm³.

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In conclusion we thank R. Tichý for assistance in the measurements and S. Roda for help in the construction of the apparatus.     

Kinetic theory of charge-density wave systems in the presence of long-range coulomb forces

The coupling between the charge-density weve condensate, and the quasiparticles and normal electrons, due to long-range Coulomb forces is investigated within the framework of the kinetic theory, for finite temperatures and in the presence of impurity scattering. The temperature dependence of the parameters, which enter the phenomenological equations for the transport in CDW systems, is determined. In the absense of normal electrons, a strong enhancement of the damping and the velocity of the phase mode is found for low temperatures, which is due to the freezing out of quasiparticles.     

Kinetic approach to modeling the radical polymerization of styrene in the presence dibenzyl trithiocarbonate

A mathematical model of the kinetics of the radical polymerization of styrene in the presence of dibenzyl trithiocarbonate by the reversible addition-fragmentation chain transfer mechanism with cross-termination of radicals and intermediates and quadratic termination of intermediates is developed. The adequacy of the polymerization mechanism underlying the model and the related mathematical formalism are tested by comparing the calculated and measured values of the average molecular-weight characteristics of resulting polystyrene.