Relationship between the diffusion rate constant and rate constant of triplet-triplet annihilation for porphyrins in liquid solutions

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70. F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 63, No. 4, pp. 613–621, July–August, 1996.     

Reasons for the difference between the rate constant of quenching of the triplet state and the diffusion rate constant of chlorophyll-like molecules

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 1, pp. 110–116, January, 1989.     

Validity of the bilinear rate equation for exciton annihilation and expressions for the annihilation constant

The validity of the well-known bilinear rate equation, used for the interpretation of exciton annihilation observations in molecular crystals, is examined on the basis of a recently constructed exact theory of the annihilation process. Experimentally attainable situations, in which the traditional equation is not applicable, are pointed out and alternative equations are given for use in such cases. Explicit expressions for the annihilation constant are given for situations in which the usual rate equation is applicable.Partially supported by the National Science Foundation under grant no. DMR 7919539     

Theoretical study and rate constant calculation for the O(3P) + C2H5CN reaction

The complicated microscopic reaction mechanisms of O(³P) with C₂H₅CN on the ground electronic state energy surface have been investigated at the G3(MP2) level of theory based on the geometric parameters optimized at the B3LYP/6-311 + G(d, p) level. Two kinds of H-abstraction and addition–elimination channels are considered, namely methylene-H abstraction, methyl-H abstraction, C-addition/elimination and N-addition/elimination. The kinetics of the title reaction have been studied using the TST and multichannel RRKM methodologies over a wide temperature range of 200–2000 K. The results show that the methylene-H abstraction process is predominant for the whole reaction. With an increase of temperature, H-abstraction from the methyl position channel should be taken into account. The C-addition/elimination process provides a few contributions to the title reaction compared with two kinds of H-abstraction channels over the whole temperature region and the N-addition/elimination channel can be negligible due to the high entrance barrier and unstable products.     

Topology of chiral superfluid: Skyrmions,Weyl fermions,and chiral anomaly

The influence of electric stochastic fields on the relativistic charged particles is investigated in the gauge invariant path integral formalism. Using the cumulant expansion one finds the exponential relaxation of the charge Green’s function both for spinless and Dirac charges.     

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.     

Resolvents,semigroups and Gibbs states for infinite coupling constant

The infinite coupling constant limit of the resolvent, the semigroup and the Gibbs state is obtained for a certain class of perturbations. As an example the infinite intrasite repulsion limit of the one-dimensional Hubbard model with nearest neighbour hopping terms is treated. This system exhibits a phase transition in the thermodynamic limit.     

A comparison of constant energy,constant temperature and constant pressure ensembles in molecular dynamics simulations of atomic liquids

Dynamic and static properties of the LJ fluid at a density and temperature close to the triple point are determined and compared for molecular dynamics computer simulations using (N, V, E), (N, V, T), (N, P, H) and (N, P, T) ensembles. As expected, the mean values of thermodynamic properties for all the different ensembles show good agreement. For the velocity autocorrelation function and the time dependence of the mean square displacement it is shown that the constant temperature and/or constant pressure algorithms used produce results which are identical, within statistical accuracy, to those obtained using the constant energy ensemble. The equations of motion are presented in a readily implementable form.     

Abstraction and exchange contributions to the rate constant of muonium+hydrogen chloride reaction

Quantum collinear rate constants for the abstraction and the exchange channels of the Mu+HCl reaction have been calculated in order to have an estimate of the relative efficiency of the two processes in promoting reactivity for this system.     

Calculation of the rate constant for the ultrasonic degradation of aqueous solutions of polyvinyl alcohol by viscometry

Ultrasonic degradation of polyvinyl alcohol (PVA) was carried out in aqueous solution at 25 degrees C. In this experiment, the effect of solution concentration on the rate of degradation was investigated. Kinetics of degradation was studied by viscometry method. The calculated rate constants indicate that degradation rate of PVA solutions decreases with increasing of solution concentration (C= g lit(-1)). The calculated rate constants correlated in terms of reverse concentration and relative viscosity of PVA solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. With increasing solution concentration, viscosity increases and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased.     

Determination of the reaction rate constant and activation energy for pressure-induced 2+2 cycloaddition of the C60 fullerene

The kinetics of fullerene solid-phase dimerization proceeding through the 2+2 cycloaddition of C₆₀ at a pressure of 1.5 GPa is investigated by vibrational spectroscopy in the temperature range 373–473 K. Kinetic curves for the formation of (C₆₀)₂ dimers are obtained using the analytical band at 796 cm^?1 in the IR spectra of the (C₆₀)₂ dimer molecule. Under the assumption that the pressure-induced dimerization of C₆₀ is an irreversible second-order reaction, the reaction rate constants are determined at different temperatures. The activation energy and the preexponential factor are found to be equal to 134±6 kJ/mol and (1.74±0.24)×10¹⁴ s^?1, respectively.     

镁铝类氢类氦类锂离子双电子复合速率研究

 镁铝类氢类氦类锂离子经中间双激发态进行的双电子复合过程在用双示踪元素谱线强度比研究ICF电子温度中占有很重要的地位。计算了双电子复合经不同Rydberg态跃迁通道的复合速率系数，并给出不同离化度的总的双电子复合速率系数的变化规律，比较了它们在不同电子温度和不同跃迁通道的异同，对研究X射线激光、等离子体温度诊断等诸多应用领域提供了有价值的原子数据。     

双波长偏振干涉型应变与温度同时测量的光纤传感器

针对保偏光纤给出了利用双波长偏振干涉型传感器同时测量应变和温度的一般理论，并通过实验证明了这一理论的可行性。对３０ｃｍ长的ｂｏｗ－ｔｉｅ型光纤的实验结果表明，在温度变化７０℃，光纤长度变化５００μｍ测量范围内，最大误差分别为±２．５℃和±８μｍ。由于这一传感器只利用了正交基模的偏振干涉，因此具有较好的稳定性。     

A study of the temperature dependence of the rate constant for the reaction of O<Subscript>2</Subscript> with surface alkoxy radicals

A method for studying the reactions of surface alkoxy radicals with O₂ at temperatures of 230 to 300 K is described. Alkoxy radicals were generated directly in the cavity of an EPR spectrometer. Surface organic radicals, prepared from paraffin wax ((CH₃)₂(CH₂) _n , n = 16–20), were applied to Aerosil particles from a solution in heptane. The Aerosil sample was placed in the cavity of the EPR spectrometer in a cylindrical cup with a central hole for pumping out gases and exposed to H atoms. In this way, it is possible observe a steady increase in the EPR signal from the surface radicals. To measure the rate constant at tropospheric temperatures, the reaction tube was placed in a Teflon jacket, through which cool nitrogen vapor was pumped. The temperature in the reactor was varied from 230 to 300 K. The recorded EPR spectra belong to the (RO) _s radical. After obtaining a stable EPR signal from the surface radicals, treatment with H atoms was stopped, additional flow of O₂ was introduced ([O₂] = 10¹⁴–10¹⁶ cm⁻³), and the reaction of O₂ with the surface organic radicals was studied by monitoring the EPR signal decay. The temperature dependence of the rate constant for the (RO) _s + O₂ → HO₂ + ketone was obtained within T = 230–300 K. The extrapolation of the data to real tropospheric conditions ([O₂] = 10¹⁸ cm⁻³) was performed.     

Pressure and temperature dependences of the dielectric constant,Raman spectra and lattice constant of SnI42

The pressure and temperature dependences of the Raman frequencies, static dielectric constant and lattice constant of the molecular crystal SnI₄, were investigated. These results are combined to evaluate the pure volume and pure temperature (i.e. volume-independent) dependences of the molecular polarizability and of the Raman-active phonon self-energies. The pressure results also allow the separation of the Raman modes into external and internal modes of the crystal; the external modes exhibit a much stronger pressure dependence, and thereby larger Grüneisen parameters, than do the internal modes. The Raman frequencies increase (decrease) with increasing pressure (temperature) whereas the dielectric constant increases with both increasing pressure and temperature, emphasizing the importance of non-volume effects. In fact, it is found that the isobaric temperature dependence of the dielectric constant is dominated by the pure temperature dependence of the molecular polarizability. The pure volume dependence of the polarizability, on the other hand, is relatively small as is perhaps typical of most molecular crystals.     

The parabolic rate constant for the high-temperature oxidation of pure or slightly alloyed nickel and the defect structure of nickel oxide

The parabolic rate constant for the oxidation of pure nickel at 1000°C is calculated on the basis of reported values of the diffusivity of defects and of a model of the defect structure of NiO considering the presence of metal vacancies of different electric charge. The dependence of the rate constant on the gas-phase oxygen activity and the profile of the concentration of the defects and of the oxygen activity through the scale are also examined. Finally the changes in the rate constant for the oxidation of nickel produced by the presence of a small concentration of a higher-valent impurity dissolved in NiO with different types of impurity distribution are examined quantitatively within the same framework, showing the great sensitivity of this parameter to doping, which is connected with the low concentration of native defects in this compound.     

From density functional steric analysis and molecular electrostatic potential to the estimation of etherification rate constant

This research extends our more recent work on the application of molecular electrostatic potential as an effective approach in describing the influence of substituent on etherification reaction rate constant of phenol derivatives. Here, in addition to electronic factor, the steric effects have also been considered for our purpose. To analyze steric effects on etherification rate constant, we use the novel energy partition scheme proposed recently by Liu [S. B. Liu, J. Chem. Phys. 2007, 126, 244103], where the total electronic energy is decomposed into three independent components: steric, electrostatic, and fermionic quantum. In this scheme, the steric potential has also been introduced. We first derive a relationship on the basis of density functional theory to show that the etherification rate constant should be proportional to the electrostatic potential on the atomic sites. Then, a bilinear function of molecular electrostatic potential and steric energy or steric potential is proposed for estimation of etherification reaction rate constants. Taking the experimental kinetics data of 30 substituted phenols, the validity of the proposed approach has been verified in position and momentum spaces. It is worth noting that the remarkable good performance of the momentum densities, which for the first time used in calculations of steric energy for a reaction, has been observed. Finally, using the relationship between new energy partition scheme and information theory, applicability of the Shannon entropy as one of the information theoretic measures is also tested for our goal and considerable results were obtained. Copyright © 2012 John Wiley & Sons, Ltd.     

NQR device for detecting plastic explosives,mines, and drugs

We describe a NQR device to detect plastic explosives, mines, and drugs and discuss design considerations.