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1.
The thermal decomposition of deuterated ethyl chloride CH2DCH2Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high-pressure limit and in the temperature range of 670–1100 K was found to be The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratio kH/kD was found to decrease with increasing pressure. The RRKM-theory calculations describe the experimental data well. The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression when kH and kD are the rate constants for the HCl and DCl channels of elimination. The Arrhenius A factors obtained at the high-pressure limit together with the temperature-dependent expression of the branching ratio provided additional experimental data for an assignment (fine-tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH2DCH2Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the transition-state model.  相似文献   

2.
The three-phonon scattering relaxation rates and their temperature exponents have been analysed in the frame of Guthrie's classification of the phonon-phonon scattering events as class I and class II events and as a result of this, a new expressionτ 3ph -1 =(B N,I+B U,Ie-θ/αT) g(w)T m I (T)+(B N,II+B U,IIe-θ/αT)g(w)T mII(T) for the three phonon scattering relaxation rates has been proposed for the first time to calculate the lattice thermal conductivity of a sample. Using the expression proposed above, the lattice thermal conductivity of Ge has been analysed in the temperature range 2–1000K and result obtained shows a very good agreement with the experimental data. The percentage contributions due to three-phonon normal and umklapp processes are also reported. The role of four phonon processes is also included at high temperatures. To estimate an approximate value of the scattering strength and the phonon conductivity, the analytical expression is also obtained in the frame of the expression proposed above forτ 3ph -1 .  相似文献   

3.
The reaction kinetics of NH2 with propylene is studied by flash photolysis in the temperature range 300-500K. The NH2 radicals are detected by resonance absorption, using a cw single mode dye laser. This method allows the detection of very small radical concentrations in a wide range of experimental conditions. The reaction of NH2 with propylene is fairly slow and seems to correspond to the addition process. The Arrhenius expression obtained is (E in kcal/mole):k(NH2 + C3H6) = 2.9 × 108 exp[-4.3(± 0.2)[RT]M?1s?1.  相似文献   

4.
The reaction of CH3OCF2CF2OCHO with Cl atom has been investigated theoretically by direct dynamics method. The BB1K hybrid functional in conjunction with the 6-31 + G(d,p) basis set has been used to optimize the geometries for the stationary points and explore the potential energy surface of the reaction. Four rotation conformers (RC1-4) of CH3OCF2CF2OCHO are identified, and they are all considered in the kinetic calculation. For each conformer, there are two kinds of H-abstraction channels and one displacement channel, and the latter one should be negligible due to involving much higher energy barrier than the former two. The individual rate constants for each H-abstraction channel are evaluated by the improved canonical variational transition-state theory with a small-curvature tunneling correction. The overall rate constant is evaluated by the Boltzmann distribution function, and a fitted four-parameter rate constant expression is obtained over a wide temperature range of 200–2,000 K. The agreement between the calculated and available experimental value at 296 K is good. The contribution of each conformer to the title reaction is discussed with respect to the temperature. In addition, because of the lack of available experimental data for the species involved in the reactions, the enthalpies of the formation (ΔH f,298°) for the reactant and its product radicals are predicted via isodesmic reaction at the BB1K/6-31 + G(d,p) level.  相似文献   

5.
The equilibrium geometry and UV-visible spectra of C70 were examined using semiempirical INDO /2 and INDO /CI methods. The results obtained are in good accord with experimental results. On the basis of correct electronic spectra, calculations of the nonlinear third-order optical susceptibility (γijkl) of C70 were performed using the INDO /SDCI method combined with a sum-over-states expression. The calculated value for <γ> (-2 ω, ω, ω, O) is 0.882 × 10?33 esu (ω = 1.91 μm), which is in good agreement with observation. © 1994 John Wiley & Sons, Inc.  相似文献   

6.
We have performed a detailed experimental study of the electroclinic behaviour in the SmA* phase above a SmA*-SmC*A phase transition. The tilt angle and polarization were measured as a function of the applied a.c. electric field, and the dielectric constant was obtained under different values of the bias field (0≤E d.c.≤ 3 V μm-1). In the region of linear regime, the behaviour observed for this SmA*-SmC*A phase transition is very similar to the one previously described for SmA*-SmC* phase transitions. The experimental results obtained under high bias field are in good agreement with the predictions of the simple theoretical model considered.  相似文献   

7.
The kinetics of the carbothermic reduction of zinc sulfide in the presence of calcium oxide and lithium carbonate has been studied by a thermogravimetric analyzer (TGA). An empirical rate expression of zinc yield has been determined from the experimental data obtained. The dependencies of the rate of zinc yield on the operating variables was found to be less pronounced for the Li2CO3 catalyzed system than those for uncatalyzed system.  相似文献   

8.
Abstract

The purpose of this studie being carried out is to define some regularities between Thin-layer and Liquid Column Chromatography; i.e. between experimental obtained and theotetical calculated RM-values and experimental obtained logk-values for some non-active organic substances in mixed binary solvents systems. It was studied the kind these correlations change with changing mobile phase compositions. The present paper is a certain aspect of new studies on possibilities of the use Thin-layer Chromato-graphy as a pilot technique for Liquid Column Chromatography (1,2). In a study on the optimization of chromatographic process it is necessary to define the correlations between RM-values which characterize the retention in TLC and k′-values which characterize the retention in in LCC.

In the paper the changes of these correlations with the changes of mobile phase compositions are studied. The conformity between theoretical calculated and experimental obtained RM-values of chromatographed substances for differemt mobile phase compositions are investigated. A good agreement between theoretical and experimental data makes possible to foresee on the basis of the correlations between log k′- and RM-values the retention in column chromatography.  相似文献   

9.
Simultaneous, quantitative, narrow-line laser absorption measurements of CN time-histories at 388.444 nm and OH time-histories at 306.687 nm have been made in incident and reflected shock wave experiments using dilute mixtures of nitiric acid (HNO3) and HCN in argon. The thermal decomposition of HNO3 serves as a rapid source of OH upon shock-heating, and the OH subsequently reacts predominantly with the HCN in the test gas mixture. The rate coefficient for the reaction was determined in the temperature range 1120–1960 K via detailed kinetics modeling of the simultaneously acquired CN and OH measurements. These data are in good agreement with lower temperature measurements of the rate of the reverse reaction (?1a) when recent values of the heats of formation of CN and HCN are used. The expression valid for temperatures 500 to 2000 K, effectively represents the experimental measurements. The estimated uncertainty of the expression for k1a is ±30%, based on the experimental uncertainties of the individual rate coefficient studies. Analysis of the decay region of the experimental OH time-histories yielded the total rate coefficient k1 (all product channels) for the reaction of HCN with OH for temperatures ranging from 1490 to 1950 K. These measurements are consistent with a previous theoretical analysis of the three primary addition-isomerization-dissociation processes for the HCN + OH reaction at combustion temperatures when the contribution to k1 from reaction (1a) is included. © 1995 John Wiley & Sons, Inc.  相似文献   

10.
A modified expression for the delayed specific luminescence of organic scintillators as a function of the incident-particle linear energy transfer is presented. Theoretical curves thus produced show a good fit to the experimental results obtained with doped polystyrene films irradiated with α particles of energy ranging from 1 to 5 MeV. The adjusted value for the bimolecular interaction parameter BT for the different concentrations of solute in the films gives consistency to the assumptions made.  相似文献   

11.
Methane is a primary product of pyrolysis of 3-chloro-l-butene at temperatures in the range 776–835°K, and from its rate of formation values have been obtained for the limiting high-pressure rate constant of the reaction These may be represented by the expression log [(k1)/sec?1] = (16.7 ± 0.3) ? (71.5 ± 1.5)/θ, where θ = 2.303RT kcal/mole. Assuming a zero activation energy for the reverse reaction and that over the experimental temperature range the rates at which a methyl radical adds on to chlorobutene are comparable to those at which it abstracts hydrogen, the activation energy for the dissociation reaction leads to a value of 83.2 ± 1.9 ckal/mole for D(H? CHClCH:CH2) at 298°K. Taking D(H? CHClCH2CH 3) = 95.2 ± 1.0 kcal/mole a value of 12.0 ± 2.1 kcal/mole is obtained for the resonance energy of the chloroallyl radical. This value in conjunction with resonance energies obtained in earlier work indicates that substitution of a hydrogen atom on the carbon atom adjacent to the double bond in the allyl radical leads to no significant variation in the allylic resonance energy.  相似文献   

12.
Using the Dyson expansion, an analytic expression is obtained for the response to a 90°-τ-90° 90'-τ′ pulse sequence of a bulk lattice of spin-1/2 particles. Particularly for larger values of τ, there are substantial deviations from simple echo-like behaviour.  相似文献   

13.
The preparation of the random photochromic copolymer poly(glycidyl methacrylate-r-1′-(2-methacryloxyethyl)-6-nitro-3′,3′-dimethylspiro-[2H-1]-benzopyran-2,2′-indoline) by ATRP is reported, which can be used for the preparation of smart materials. Narrow homopolymers obtained from glycidyl methacrylate (GMA) are prepared when HMTETA-copper bromide and ethyl 2-methyl-2-bromo-propionate are used as the catalytic system with methyl-ethyl-ketone at 50°C. By using a molar ratio of 1:1 ligand:initiator, good correlations between experimental and theoretical molecular weights and narrow molecular weight distribution are obtained. These experimental conditions are also employed for the copolymerization of GMA with a photochromic monomer, where again good control of the polymerization reaction is obtained. The copolymer is fully characterized by spectroscopic techniques. The reactivity ratios are calculated according to the extended Kelen-Tüdos method, while the composition of the copolymer is calculated by NMR. Determination of r GMA and r PHM gives a value of 0.985 for GMA and 0.596 for the photochromic monomer.  相似文献   

14.
In this work, we describe for first time, the structure and magnetic characterization of the one dimensional catena cis-[Ni(μ-ox)(H2O)2] (1), which was obtained by solvothermal synthesis. Cis-[Ni(μ-ox)(H2O)2] crystallizes in a C2/c spatial group. The asymmetric unit contains only one type of nickel atom, oxalate ligand and water molecules. The chain backbone is constructed by the bis-chelating coordination mode of the oxalate ligand, presenting a zigzag chain in the [1 0 1] direction. The nickel ions have a distorted octahedral geometry, surrounded by six oxygens, four of them from two different oxalate ligands and the other two from the cis-coordinated water molecules. Thermal dependence of the magnetic susceptibility of (1) was studied in a temperature range of 2.5-255 K, at applied fields of 0.10 and 0.25 kOe. The plot of χMT(T) shows antiferromagnetic interactions between the Ni(II) centres. The experimental data were fitted between 255 and 30 K, using an empirical expression for a chain of equally spaced Ni(II) centres. The best fit of the experimental date gave a J value of −57 cm−1, which is much higher that the obtained for the trans-analogue. Irreversibility between ZFC and FC measurements below 9 K was observed, indicating some kind of magnetic ordering.  相似文献   

15.
The cyclooctatetraenyl dianion (C8H82−) π-conjugated system forms a stable complex system with alkali and some transition metals. The results of vibrational analysis for C8H8M2 (M = Na, K) complexes were reported here. The geometries of C8H8M2 (M = Na, K) were optimized using ab initio (HF, MP2, CCSD(T)) and DFT (B3LYP) methods with 6-311G** and 6-311++G** basis sets and the harmonic frequencies were obtained. To reproduce and compare with the experimental values the structurally similar molecules C5H5M (M = Na, K) and benzene were studied. The scale factors obtained from these systems were applied to predict the experimental frequencies of C8H8M2 (M = Na, K). The force field and vibrational spectra are analyzed and the most probable assignments are proposed for all the fundamentals based on the potential energy distribution.  相似文献   

16.
A stepwise segment-by-segment cluster development of the interaction energy of two polymer coils at given distance leads to a closed expression, describing the second virial coefficient A2 in terms of certain intersegmental contact probabilities. An approximate expression for A2(α,z) in good solvents is then derived by using the uniform segment cloud model; the result being equivalent to that obtained by Flory. This expression is combined with the author's theory for α2(z) to give A2(z), and then with a subsequent adaptation of that theory to polyelectrolytes, to derive the dependence of A2 on ionic strength. The α2(z) and A2(z) equations are both compared with recently reported experimental data for NaPSS.  相似文献   

17.
The kinetics of gamma-radiation-induced free-radical chain reactions in solutions of carbon tetrachloride in mixtures of varying composition of cyclohexane and n-hexane was investigated in the temperature range of 296°–413°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated alkyl radicals with the solute. The kinetics of the following reactions were studied: The following rate expression was obtained: The error limits are the standard deviation from the least mean-square Arrhenius plots. The present results, combined with previously measured activation parameters for hydrogen-atom abstraction from c-C6H12 and n-C6H14 by CCl3 radicals relative to CCl3 combination, afford experimental evidence that the decay of trichloromethyl species in alkane solutions is a diffusion-limited process. The thesis that activation energies of reactions (4) and (5) in the liquid phase are equal to their respective values in the gas phase is confirmed.  相似文献   

18.
The thermochemical kinetics formulation of conventional transition state theory has been applied to metathesis reactions of H atoms with a series of alkanes in order to provide a sound framework for the intercomparison of experimental data, and also to extrapolate rate coefficients to temperature regimes that may lie beyond the range of experiments. The calculations require a value for the rate coefficient at some temperature, necessitating a discussion of the extant experimental data and their reliability. The procedures are described, the results of the calculations are presented, and their agreement with experimental data (for methane, ethane, propane, butane, pentane, isobutane, cyclopropane, cyclohexane, neopentane, neooctane, and 2,2,3-trimethylbutane) is discussed. A general expression for reactions of H with large (more than 4 carbons) alkanes is proposed: where np, ns, and nt are the numbers of primary, secondary, and tertiary H atoms available for abstraction.  相似文献   

19.
《Fluid Phase Equilibria》1999,166(1):111-124
An equation for the self-diffusion coefficient in a polyatomic fluid is presented as a sum of three friction coefficient terms: the temperature-dependent hard-sphere contribution, the chain contribution and the soft contribution. This equation has been developed by using the molecular dynamics simulation data for the HS chain fluid and the expression for the Lennard–Jones (LJ) fluid proposed by Ruckenstein and Liu. The real nonspherical compounds are modeled as chains of tangent LJ segments. The segment diameter σLJ, segment–segment interaction energy εLJ and chain length N (the number of segments) are obtained from the experimental diffusion data. The equation reproduces the experimental self-diffusion coefficients with an average absolute deviation (AAD) of 3.72% for 22 polyatomic compounds (1081 data points) over wide ranges of temperature and pressure. The results have been compared with that of the rough LJ (RLJ) equation. To minimize the number of the fitting parameters, the energy parameter εLJ is estimated using a correlation obtained from viscosity data. The equation with two parameters gives an AAD of 4.72%.  相似文献   

20.
The lattice thermal conductivities of Mg2Ge and Mg2Si have been analysed in the entire temperature range 2–1000 K in the frame of a new expression for the phonon-phonon scattering relaxation rate proposed by Dubey as $$\tau _{3ph}^{ - 1} = (B_{N,I} + B_{U,I} e^{ - \theta /\alpha T} )g(\omega )T^{m_I (T)} + (B_{N,II} + B_{U,II} e^{ - \theta /\alpha T} )g(\omega )T^{m_{II} (T)}$$ based on the Guthrie classification of the phonon-phonon scattering events, and a very good agreement has been obtained between the calculated and experimental values of the lattice thermal conductivity for both samples in the entire temperature range of the study. The separate percentage contributions due to three-phonon normal and umklapp processes towards the three-phonon scattering relaxation rate have also been studied. The role of the four-phonon processes has been included in the present analysis.  相似文献   

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