Slowing down of oxygen migration in the processes of radical oxidation and of phenanthrene phosphorescence quenching in methanol glasses at 90 K

The hydroxymethyl radical oxidation kinetics follows the second-order equation with a time-dependent rate constant, K(t). The annealing effect is described by way of dividing K(t) into two factors, one of them depending on the preliminary annealing time (τ): K(t) = K₁(t + τ)K₂(t). The time dependence of both factors is fairly well approximated by the power functions: K₁(t + τ) ≈ (t + τ)^−0.18 and K₂(t ≈ t^−0.26. The oxygen quenching of phenanthrene phosphorescence follows an exchange mechanism, with the static conditions setting in at 77 K. At 90 K oxygen diffusion adds to the quenching efficiency. The time of oxygen jumps (τ_j) and its time dependence under the matrix annealing at 90 K are determined by comparing the theoretical 1/τ_j dependence of the quenching volume with experiment. The 1/τ_j(τ) is well described by the power function τ^{−0.18 ± 0.02)}. The annealing time functions of the oxidation rate constant and of the inverse jumping time are similar. The oxidation rate constant and the diffusion constant coincide in the order of magnitude. Consequently, the slowing down of oxygen migration contributes essentially to the time dependence of the rate constant.     

Brief review related to the foundations of time-dependent density functional theory

The electron density n(r,t), which is the central tool of time-dependent density functional theory, is presently considered to be derivable from a one-body time-dependent potential V(r,t), via one-electron wave functions satisfying a time-dependent Schrödinger equation. This is here related via a generalized equation of motion to a Dirac density matrix now involving t. Linear response theory is then surveyed, with a special emphasis on the question of causality with respect to the density dependence of the potential. Extraction of V(r,t) for solvable models is also proposed.     

Mutual annihilation of triplet excitons in a nearly one-dimensional system: 1,4-dibromonaphthalene

The analysis of the variation with incident flux of the time dependence of the delayed fluorescence in conjunction with the determination of the absolute ground state-first excited triplet absorption coefficients at room temperature, yields the value of γ_tot = (5.5 ± 2.0) × 10^?12 cm³ s^?1, for the total triplet-triplet annihilation rate constant in 1,4-dibromonaphthalene crystals. The one-dimensional mutual annihilation rate constant for the triplet exciton motion restricted to linear chains along the crystal c axis is γ¹_tot = (1.0 ± 0.4) × 10³ cm s^?1. The results are discussed in terms of recent theories of mutual annihilation of triplets in one-dimensional systems.     

Bremsstrahlung emitted during (n;t)-reactions in light atomic systems

Bremsstrahlung emitted during (n;t)-nuclear reactions in light atoms and ions is discussed by using both the classical and quantum-mechanical approaches. In particular, the spatial and angular distributions of the emitted radiation and its spectrum are considered in detail. It is shown that the total radiation I(t) rapidly decreases with time I(t)∼t⁻⁴ at large t. The spectral density of the emitted bremsstrahlung is also studied. In general, bremsstrahlung emitted during (n;t)-nuclear reactions in the fast ions and atoms can be used to study the electron–electron position correlations in these systems. The approach developed in our present study can also be applied to describe the emission of bremsstrahlung during (n;p)- and (n;α)-nuclear reactions in light atoms, spontaneous and neutron-stimulated nuclear fission in heavy atoms.     

Study of Scaling Exponents of the Surface Evolved in 2 + 1 Dimension through Competitive Growth between Random Deposition and that with Surface Relaxation

Rough surface develops through computer simulation by competition between growth mechanism random deposition (RD) with a probability of occurrence p and growth mechanism random deposition with surface relaxation (RDSR) with a probability of occurrence 1 − p, on L × L square plane for system size L to record the statistical average of time variation of surface roughness W(L, t) and average height H(t) for the model for specific values of L and p. Other than the pure RD model, the entire evolution may be divided into three regions separated by two specific cross-over times t_x and t_sat. The value of interface width at saturation W_sat depends on both L and p. The first growth exponent β₁ increases exponentially with an increase in p and does not depend on L. The values of the second growth exponent β₂, roughness exponent α, dynamic exponent z( = α/β₂ ), and α + z are 0.0234 ± 0.0008, 0.0506 ± 0.0065, 2.1577 ± 0.0073, and 2.2083 ± 0.0138 respectively and they show no dependence on L and p values. Value of the first cross-over time t_x increases exponentially with an increase in p and does not depend on L. Value of the second cross-over time t_sat increases with an increase in both p and L values. The average growth velocity is unity for the model and is independent of both L and p. For the model, the growth velocity is unity and the fractional porosity is zero. The scaling exponents show some deviation from the relevant universality classes and depend on competitive growth probability for this model. No finite-size effect is present in the model.     

C,N-chelated hexaorganodistannanes, and triorganotin(IV) hydrides and cyclopentadienides

Triorganotin(IV) hydrides and cyclopentadienides as well as hexaorganodistannanes containing the moiety L^CN (2-(N,N-dimethylaminomethyl)phenyl-) as chelating ligand and phenyl, n-butyl or t-butyl substituents were prepared and characterized by NMR and XRD. The compounds reveal trigonal bipyramidal geometry around the central tin atom except for the distannanes in which the tin atom has tetrahedral configuration. The di-n-butyl distannane cannot be oxidized by oxygen or heavier chalcogens and give no tin radical when irradiated by UV light or treated with the TEMPO - free radical at room temperature. L^CN(t-Bu)₂SnH undergoes reaction in solution toward the corresponding distannane. The hydrostannation reaction of L^CN(n-Bu)₂SnH with ferrocenylacetylene was investigated. The CO₂ activation by L^CN(n-Bu)₂SnH was also examined.     

Determination of the electric field and anomalous heating caused by exponential pulses with aluminum electrodes in electroporation experiments

Electroporation is well known to depend non-linearly on the magnitude and duration of the change ΔU(t) in transmembrane voltage. In the case of cell suspension experiments, an electric field E_e(t) within the electrolyte causes ΔU(t), which is governed by both the size and shape of a cell, and also by E_e(t). It is therefore important to determine the magnitude and time dependence of the electric field to which cells are actually exposed in electroporation experiments. This can be significantly different from the nominal field E_n, which is calculated by using electrode voltages and geometries alone. Throughout we used single, nominally exponential pulses with time constants τ_pulse ranging from about 0.6 to 5 ms and found that E_e was always less than E_n. In order to determine the actual electric field pulse, we measured the voltage across the electrodes, the current through the cuvette, the temperature rise of the pulsing medium, and the voltage across two special electrodes placed within the cuvette. From these measurements we calculated the field strength inside the cuvette using two different methods. In addition, we compared the measured temperature rise with that expected from the electrical power dissipation. In some cases there was much larger (“anomalous”) heating, due to interfacial electrochemical heat production; for one pulsing solution T_e(t) was about 30 K larger than expected. These effects are important for experiments aimed at elucidating the electroporation mechanism, comparing results obtained under different conditions, and guiding applications.     

The exciton—phonon interaction for triplet exciton bands of organic solids: An experimental and theoretical study

Very high resolution optical data on the temperature dependences of the Davydov component absorption profiles and polarization dependent one-phonon structures associated with the lowest triplet exciton band of anthracene are presented along with a theoretical framework for their interpretation. The interpretation of the one-particle exciton—phonon transitions involving both one-phonon creation and annihilation (cold and hot phonon transitions) is entirely consistent with the analysis of the T-dependent dephasing of the lowest zero-phonon Davydov transition in terms of two mechanisms: delocalized exciton—delocalized phonon scattering operative for the low frequency (< 30 cm^?) phonons which undergo no lattice distortion and: Raman like phonon scattering operative for the higher frequency phonons which do. It is the latter which leads to the identical T² linewidth dependences of the two Davydov components in the high T limit. The former scattering is dominant at the lowest temperatures. In addition, the, marked and polarization dependent mirror symmetry breakdown between the hot and cold one-particle transitions can be nicely understood in terms of interferences occurring between the Condon and phononic (from the dependence of the pure exciton transition dipoles on phonon coordinate displacement) contributions to the one-particle transition dipoles. It is argued that our findings for anthracene should prove useful for triplet exciton bands in other organic solids.     

NMR in metal cluster compounds compared to glasses

The field and temperature dependence of the³¹P nuclear spin lattice relaxation rate in the metal cluster compound Ru₅₅(P(t-Bu)₃)₁₂Cl₂₀ follows a power law: 1/T ₁ ∝T ⁿ B ^?m , withn=1.5±0.1 at 3.25 T andn=1.3±0.1 at 6.45 T;m ? 1.4. Such dependences have so far only been observed in inorganic glasses and been attributed to two level systems. The correspondence suggests that the relaxation rate is due to interaction of theP-nuclear moment with electronic spins of stochastically moving charge carriers, which are thought to be responsible for the electrical conductivity through hopping between neigboring cluster molecules.     

Exciton dynamics in molecular crystals from line shape analysis. Time response function of singlet excitons in crystal anthracene

From an accurate measure of the temperature dependence of the line shape function ω ?₂ (ω) information is obtained about the time behaviour of the response function of singlet excitons of small wavevector encompassed by the (0-0) band of the 4000 A Å transition in crystal anthracene. An apparatus to determine the reflection band profile with high accuracy needed to give correct ω ?₂ (ω) data is described. Although the data analysis is not without problems, there is strong evidence that the time behaviour of excitons in this transition is characterized by a stochastic collision time τ_c. The temperature dependence of τ_c is consistent with a model in which the intermolecular phonons are weakly coupled with the exciton created by either b or a polarized light. Phonon annihilation is predominant for the b-polarized transition but both phonon creation and annihilation are active for these polarized transition. The similar values of the exciton—phonon coupling function for both polarizations may indicate either the importance of higher multipole terms for that function or strong interband scattering. The relationships between τ_c and parameters from other experimental results on singlet excitons in crystal anthracene are considered. The results may allow for a better understanding of the mechanism of exciton—phonon coupling in crystals.     

Ligand effects in the substitution chemistry of cis-bis(piperidine)tetracarbonylmolybdenum(O). A molybdenum-95 NMR study

Molybdenum-95 NMR chemical shifts are reported for a series of Mo(O) compounds of the type Mo(CO)₄(pip)_2−nL_n(n = 1,2; L = substituted pyridine ligands). The σ(⁹⁵Mo) values correlate well with the pK_a values for the substituted pyridines; for the n = 1 series, σ (⁹⁵Mo) ranges from − 1053 ppm (pK_a = 1.86 for 4-CN) to − 1120 ppm (pK_a = 9.61 for 4-NMe₂). The effects of solvent polarity and some in situ reactivity studies are described and the nature of the MoL bond compared to that with piperidine and some other ligands is discussed.     

Lattice enthalpies and magnetic loops in lanthanide iron garnets,Ln3Fe5O12

Experimental lattice enthalpies Δ_LH^θ of lanthanide iron garnets Ln₃Fe₅O₁₂ (LnIGs) with Ln = Ce − Lu, have been determined from the Born–Haber thermochemical cycle. The results have been compared with those reported by other authors using numerical simulation or an empirical equation. The lattice enthalpy of PmIG has been predicted by linear interpolation between Δ_LH^θ of the adjacent NdIG and SmIG. It has been found that the partial derivative (∂Δ_LH^θ/∂V_m) for the series of LnIGs corresponds by magnitude and dimension to an upper limit of their rigidity. New effect of magnetic loops has been noted in the same series in the dependence of the lattice magnetic entropies on the effective magnetic moments (theoretical and experimental values).     

Translocation of a protein-like chain through an interacting channel

The effect of channel-protein interaction on the translocation of a protein-like chain through a finite channel under certain electric field was studied by using dynamical Monte Carlo simulations.The interior behavior of chain conformation under different interactions was investigated,such as the number of monomers outside of channel n_out,monomers inside of channel n_m,mean-square radius of gyration〈S²〉and the average energy〈U〉.It shows that with strong attractive interaction,the translocation is more difficult than moderate interaction.At the same time,the dependence of translocation time with different interactions shows that moderate repulsive interaction(ε_cp= 0.5) accelerates the translocation.Although the waiting time for successful translocation ofε_cp = 1.0 is the longest,the average translocation time is not very large.It is far smaller than that ofε_cp=-1.0.The probability distributions of translocation time p（t’） and the probability distributions of three duration times p（t₁’）,p（t₂’） and p（t₃’） were all discussed.Log-normal distributions are found.All these findings will strengthen the understanding of protein translocation.     

Mean polarizability of molecules and anisotropy of the Lorentz tensor upon a nematic-smectic a phase transition: Their behavior in a homologous series

Experimental values of the mean polarizability of molecules, [`(g)]\bar \gamma , and components of the Lorentz tensor, L <sub>j</sub> , in the nematic and smectic A phases are obtained for a homologous series of n-alkyl-p-(4-ethoxybenzylideneamino)-α-methylcinnamates. Dependences of the [`(g)]\bar \gamma and L _j values on the mesophase temperature, the orientational order parameter S of molecules, and the number n in the homologous series are revealed. The quadratic dependence of [`(g)]\bar \gamma (S) in the nematic and smectic phases is established that is invariant with respect to the nematic-smectic A transition. Polarizability densities of the molecular core and the alkyl chain are found from the monotone decreasing dependence [`(g)]\bar \gamma (n)/v (where v is volume per one molecule) in the smectic phase. The presence (or absence) of the odd-even alternation of L _j (n) in the nematic (smectic) phase is shown. A monotone decrease in the Lorentz tensor anisotropy L with an increase in n is revealed in the smectic phase, and limiting values L _j (n → ∞) are determined.     

High-temperature heat capacity of YbAl3(BO3)4

The isobaric heat capacity C _p (T) of YbAl₃(BO₃)₄ grown by spontaneous crystallization from solution (100 ? n) wt % (Bi₂Mo₃O₁₂ + 2.5% B₂O₃ + 0.75% Li₂MoO₄) + n wt % YbAl₃(BO₃)₄ is studied experimentally in the region of 344–1016 K. It is established that there are no extrema on the C _p (T) dependence, and the obtained data can be described using the Berman-Brown polynomial. The temperature variations of enthalpy and entropy are calculated from the C _p (T) dependence.     

Description of the shape of thermoanalytical curves : Part 2. Simulation of Peak Shape from Kinetic equations

Differential thermoanalytical curves were simulated with the commonly used kinetic equation dα/dt = A exp (?E/RT)·(1 - α)ⁿ; noise and baseline components were added. Empirical parameters describing peak shape were calculated. Comparison of the results with those of experimental differential scanning calorimetric curves show that sufficiently different sets of the three kinetic parameters can be distinguished on the basis of peak shape. The effects of noise and baseline choice are discussed in detail.     

Heat capacity, enthalpy, entropy, and gibbs energy of terbium diboride as determined from calorimetric measurements within 5–300 K

The heat capacity at constant pressure C _p (T) of terbium diboride synthesized from elements via an intermediate hydride phase was studied experimentally within 5–300 K. A ferromagnetic phase transition manifests itself in the C _p (T) dependence as a sharp maximum at 142.4 ± 0.1 K. The C _p (T) dependence was used to calculate the tempreature dependences of the enthalpy, entropy, and the Gibbs energy and to determine the parameters of the electronic, lattice, and magnetic contributions to the heat capacity of TbB₂.     

Cadmium ion reduction at mercury electrode in aqueous KCl solution in presence of adsorbed polyvinyl alcohol

The influence of polyvinyl alcohol on the kinetics of cadmium ion reduction in 1M aqueous KCl solution at the dropping mercury electrode was investigated using the impedance method. It was found that small additions of PVA did not change the diffusion coefficient much, but affected only the rate of charge transfer process. The electroreduction of cadmium in the presence of PVA became less reversible. The standard rate constant dependence on coverage degree is described by the following equation: k_s=k_s0(1?ν)ⁿ, where n=2.     

Photochemical isomerization in the absence of a potential barrier

The photoisomerization dynamics of the dyes pinacyanol, 1,1'-diethyl-4,4'-eyanine and t-stilbene in n-alcohol solutions has been studied by picosecond absorption spectroscopy. The dyes are found to isomerize without any potential barrier in the excited state. The viscosity and temperature dependence of the relaxation rates of pinacyanol and t-stilbene agree with predictions of theoretical models, whereas for 1,1'-4,4'-cyanine more complex behaviour is observed and possible reasons discussed. An excitation wavelength dependence of the isomerization rate for 1,1'-4,4'-cyanine was also observed; the isomerization lifetime varies by a factor 2–3 over the absorption band. Such a dependence is predicted from the theoretical models.