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1989 Volume 5 Issue 6
The superconducting phase Tl_2Ba_2CuO_6 with onset T_C 85 K and zero resistivity at 61 K has been prepared. The unit cell is body-centred tetra nal, space group I_4/mmm, lattice parametrs a=0.3866(1) nm, c=2.3180(3) nm. The relation between structural features and its superconductivity was discussed.
The photochemical oxidation studies of four Rh_2L_4(d~7—d~7) complexes with RCl were reported for the first time. All of them have different kinds of the dinitrogen bridging ligands:compound 1 and compound 2 are two geometric isomers of Rh_2(ap)_4, ap=2-anilinopyridinate, 2,2-trans and 4,0; compound 3 is Rh_2(dpb)_4, dpb=N, Ndiphenylbensamidinate; compound 4 is Rh_2(dpf)_4, dpf=N, N-dipynylformamidinate. RX are CCl_4, CHCl_3, CH_2Cl_2, C_2H_4Cl_2, C_6H_5Cl and C_6H_4ClCN, respectively. The four complexes of Rh_2L_4(d~7—d~7) complexes under a photoinduced halogen abstraction and an one-electron transfer process by irridiation in the visible region. Quantum yields of formation oxidized complexes were determined for the four complexes. It is showed that the quantum yields depend on irradiation wave-length, solvent and axial ligand. Compound 1 is considerably more photochemically active than another compounds. Preliminary flash photolysis studies in the presence of alkyl or aryl halides show that an irreversable electron transfer occurs. However in the presence of nonreactive acceptors such as acetonitrile, reversible electron transfer occurs. However in the presence of nonreactive acceptors such as acetonitrile, reversible electron transfer occurs. Photolysis products were determined by fast atom bombardment mass spectroscopy, and were compared with the electrochemical products. The results of photochemistry were discussed.
The behaviors of cyanide and thiocyanate on copper electrode were studied using cyclic voltammetry and in-situ FTIR spectroelectrochemistry. When potential was shifted from -1.60 to 0.30V(vs.SCE), three bands near 2076, 2094, and 2170 cm~(-1) were recorded within the wavenumber range 2030—2230 cm~(-1) in 0.5 molL~(-1) NaCN+0.5 molL~(-1) NaF. The bands near 2070 and 2170cm~(-1) were due to solution species CN~- and surface deposited CuCN respectively. The band near 2094 cm~(-1) was attributed to absorbed CN~- and complex Cu(CN)_3~(2-). In 0.5 mol L~(-1) NaSCN+0.5 mol L~(-1) NaF, three bands near 2060, 2117 and 2170 cm~(-1) were observed in the potential range metioned above, and attributed to the IR absorption of solution species SCN~- (2060 cm~(01)), absorbed SCN~- (2117 cm~(-1)) and CuNCS (2170 cm~(-1)) which was the product of electrode reaction.
We have studied the Surface Enhanced Resonance Raman Scattering (SERRS) spectra of xanthene dye molecules (R110, RB, SRB, R6G, R101 and SF) adsorbed on chemical deposited silve-island films. In this paper, the experimental conditions for SERRS have been described, the assignments of Raman scattering bands have been done, and the influence of resonance, surface enhancement and the preparations of substrates on the characters of SERRS and on the enhancement of Raman scattering cross-section have also been discussed. The results show that SERRS is a new and effective method for studying the intense fluescence dye molecules and their interaction with metal surface.
This paper presents two types of ehulliometer: CP--Ⅰ and CP-Ⅱ, shows in detail the ideas and principles of each unit of the ebulliometers.The new ebulliometers, which are the multipurpose instruments designed for mceting the more needs of measuring vapour-liquid equilibrium data, have the characteristics of both the ebulliometer and the still. As stills, they can be used to measure vapour-liquid equilibrium data of the miscible system and the partially miscible one; and as ebulliometers, to meet the pseudo-static, the exchanging, and the boiling point analysis methods for measuring vapour-liquid equilibrium data. In particular, type CP-II, which has the functions of determining factor of the holdup and the reflux ratio, is used to measure the terminal values (K~∞, r~∞). The functions of each unit and the characteristics of the instruments are tested and the expected results are obtained.
The additive-oxidation of hydrogen in olefin hydroformylation catalyzed by cobalt carbonyl has been studied by using the ASED-MO mothod,in which the quantum chemical calculation was employed to the investigation the molecular geometries of reactants and products, as well as the energy variations with the proceeding of reaction.
From the calculated results, we have proposed that two reactive pathway be suitable for the reaction. The energy surfaces for both pathways were obtained respectively, and then the reaction process has been further disscussed in the light of calculating results.
Transient absorption spectra in the photocolouration of 1-n-octyl-3,3-dimethylindolino-2,2'-spiro-5',6'-(2-bromo-4-nitro-benzo)-pyran (SPP1), 1-n-octyl-3,3-dimethyl-indolinn-2,2'-spiro-5',6'-(4-nitro-benzo)-pyran (SPP2), 1-n-octyl-3,3-dimethylindolino-2,2'-spiro-5', 6'-(2, 4-dinitro-benzo)-pyran (SPP3) and 1-n-octyl-3,3-dimethylindolino-2,2'-spiro-5', 6'-(2-chloro-4-nitro-benzo)-pyran (SPP4) in toluene and eyclohexane were investigated with nanosecond laser photolysis. Several certain intermediats and an aggregate were observed. The mechanism of the isomerization involves not lnly triplet process but also singlet process.
X-ray crystallography and computer-assisted conformational analysis and computer graphics studies were performed for seven Fentanyl-type potent a nist of opiate receptor. The results obtained demonstrate that there is a od agreement between the experimentally determined (by X-ray) and the calculated (by DPCILO) conformation of Fentanyl derivatives. The orientation of the N-phenylpropanamide with respect to piperidine ring plays an important role in the binding of Fentanyl-type analgeties to the opiate receptor.
When the N-phenethyl substituent is the antiperiplanar conformation and torsion angle (C_(11)—C_(12)—N_(15)—C(16)) is about 100°, Fentanyl derivatives may interact equally well with the recetor. On the basis of conformational analysis and molecular graphics fit the model for the requirements of the receptor has also been discussed.
For a RDE system not to be coupled with homogeneous chemical reactions, the Laplace transform of the general convective diffusion equation is
s~-c_j(x, s)-c_j~*=D_l ~2~c_j(x, s)/ ~2x-V_x c_j(x, s)/ x
in which, s is the Laplace transformation variable complementary to time t, c_j~* is the bulk concentration of species j, ~-c_j(x, s) is the Laplace transform of concentration c_j(x, t), D_j is the diffusion coefficient, x is the axle center of RDE, V_x is the solution velocity at x direction, we solve this equation with a canonical perturbation method for small variables |vs/D_(jω)| and |D_(jω)/vs|, here v is the. kinetical viscosity of the electrolyte solution, and ω is the rotation speed of RDE. We get two equations
~c_j(0, s)/ x=[c_j~*/s-c_j(0, s)][(s/D_j)~1/2+1/δ_j exp(-1.05δ_j(d/D_j)~1/2]
or (0.7% relative error)
~-c_j(0, s)/ x=((s/D_j)~1/2[c_j~*/s-~-c_j(0, s)])/(1-[1+1.07δ_j(d/D_j)~1/2]exp[-2.07δ_j(s/D_j)~1/2])
(1% relative error)
in which δ_j is the limiting diffusion layer thickness of the steady state at RDE.
Upon the last two Laplace, we are able to deal with nonstationary processes in a RDE system with Laplace transformation procedure.
For the large-amplitude potential step process, the current equation obtained is
i(t)/i_1=(π(D_Ot)/δ_O~2)~-1/2+erfc[0.525((D_Ot)/δ_O~2)~-1/2
where i_1 is the limiting current of the steady state at the RDE. The calculated value is closed to the theoretical results of Siver and Bruckenstein et al.
For the pulsed current process, we obtain the limiting pulsed current equation
i_1/i_(p1)=T_1/T+0.830((D_OT)/δ_O~2)~1/2(1-T_1/T)~1.011(0.9>T_1/T>0.01, ((D_OT)/δ_O~2)<0.34)
in which, i_(p1) is the limiting pulsed current, T is the cycle time of the pulsed current, T_1 is the pulsed time. The calculated value is closed to the theoretical and experimental results of Viswanathan et al.
Two methods to analyze polarization curves of Ni-Fe alloy codeposition were established by using ring-disk electrode based upon the limiting electricity quantity of electrooxidation of Fe~(2+) ions on ring electrode and the shielding effect on the above ring electrode process by electrorcduetion of Fe~(2+) ions on disk electrode respectively. The kinetics of Ni-Fe codeposition on Hg, Ni, Fe and Ni-Fe alloy electrodes had been investigated. The results showed that Ni~(2+) and Fe~(2+) were electrodeposited on Hg electrode with the same kinetics as they were electrodeposited individually, but Ni~(2+) was electrodeposited activably on Fe electrode, and the electrodeposition of Fe~(2+) on Ni electrode was inhibited. The mechanism of codeposition of Ni—Fe alloy had been discussed.
The kinetics of oxidation of methanol to formaldehyde on Mo-Bi-Ce/SiO_2 catalyst has been investigated in an external recirculation gradientless reactor. The kinetic data can be described by a two-stage redox model. The parameters of the kinetic equation were estimated by the linear least square method. The m-order with respect to methanol and n-order with respect to oxygen depended on the reaction temperature and m+n=1 (the sum of m and n is close to 1). The change of reaction order was interpreted by the kinetics of redox mechanism. XPS results which come from different treated catalysts verify the redox mechanism mentioned above.
Ab initio quantum chemical method has been used to study the proton transfer of the L-form of 2-hydroxyethenyl-1-oxy(C_2H_3O_2) radical. The geometries of the C_2H_3O_2 radical as well as the transition State of proton transfer have been optimized at the level of UHF/3-21G. Vibrational analysis has been made of tnese two configurations to obtain the vibrational frequencies, by means of which the entropy of activation of the proton transfer reaction of C_2H_3O_2 radical has been evaluated.
In order to get better energetics, the energies of some points on the Intrinsic Reation Corrdinate (based on the geometries of UHF/3-21G) have been recalculated at the level of UMP2/3-21G~+ (diffusion function has been added to the H atom participating the transfer). Potential energy profile and tunnel effect correction were obtained by using this proton transfer reaction was calculated to be 7.4×10~(11) s~(-1).
The intramolecular hydrogen bond stabilization energy and H-bond length H(1)O(5) obtained at the optimized geometries of UMP2/3-21G~+ are 19.2 kJ mol~(-1) and 0.2057 nm respectively.
Using the equilibrium structures, energies and vibrational frequencies of formyl chloride, its transition states and products for its isomerization and photodecomposition, which had been obtained by Han and Liu, and using the kinetic computer program written by ns, we have calculated their thermodynamic functions, the changes of Gibbs functions and the equilibrium constants,the rate constants as well A factor of the titled reactions. Furthermore, the mechanism of the reactions has been analysied. Our calculated results are in od agreement with the experimental ones.
In addition, as viewed from describing chemical reactivity, the peper gives how to use the results of ab initio MO theory calculating chemical equilibrium constants and kinetic rate constants.
A new method developed the double layer interaction free energe for two spherical particles by us, is extended, to the case of two cylindershape colloidal particles having equal radii(b). When a parallel body of the cylinder moves around other parallel body of cylinder, each orientation of anisometrie cylinder was taken account in calculating the interaction, energy, it is the average repulsive energy. This paper reports Monte Carlo (MC) computation on the two cylindershape colloidal particles in all relative position. MC simulation agrees with our results for κb=0.5 and κb=3.
Construction and characterization of a novel long pathlength thin-layer UV-visible spectroelectrochemical cell are reported. The cell utilizes a cylindrical Teflon electrode which is machined to have a 10×2×0.8 mm thin-layer chamber in the lower end, in which a platinum plate working electrode is positioned. As the electrode is plugged into the cell, the walls of the cell close two ends of the thin-layer chamber and serve as optical windows of 10 mm light path-length. A light transparent jacket is provided for temperature controlled experiments. Well behaved thin-layer cyclic voltammograms and spectral responsed for ferrocene redox reaction were obtained in dichloroethane and toluene solutions.
The solubilization of pyrene in perfluorooctoate micelles with addition of N(C_2H_5)_4Br,N(C_4H_9) (C_2H_5)_3Br and N(C_4H_9)_4Br have been studied by steady fluorescence measurements. The results show that the perfluorooctoate micelles can solubilize pyrene, and the maximal amount of pyrene solubilized is increased considerably on the addition of the alkylammonium bromide; the perfluo-micelles quench the fluorescence of pyrene solubilized into it; the solubilizing sites are all near the stern layer of the micelles, and can be changed by the addition of the alkylammonium with different hydrophobicity due to the stronger interaction between pyrene and the hydrocarbon of the ammonium than that between pyrene and fluorocarbon chain of the surfactant.
In the model of ore nator of B-Z reaction, the stability of dynamic equations of system with temperaure as a parameter is investigated and the oscillation area is determined through the relation of k_i(T) to T. For the first time,we explained the sensitivity of the oscillation of B-Z reaction to the variations of temperature according to the results of experimental and theoretical analysis.
In this paper we reported KrF laser induced telomerization reaction of BrC_2F_4Br+C_2H_4. The main products are adducts BrC_2F_4C_2F_4Br, BrC_2F_4C_4H_8Br and others (BrC_2F_4C_2H_3, erc). The Influence of the reaction conditions (pressure of reactants, fluence of laser, reaction temperature and others) has been investigated.
Using a low angle laser light scattering photometer (LALLS) the second virial coefficients(A_2) of ring-shaped and linear polystyrene (RPS and LPS) samples were determined in both toluene and butanone solutions. The A_2 of RPS in the od solvent (toluene) is smaller than that of LPS with the same molecular weight, but in the poor solvent (butanone) these two are very close. For RPS in the molecular weight range of 4×10~4——2.2×10~5, we have
A_(2r)=1.28×10~(-2)M_w~(-0.283) (Toluene 25 ℃)
and A_(2r)=5.06×10~(-2)M_w~(-0.273) (Butanone 25 ℃).
According to the theromodynamical formula of chemical equilibrium, for the reaction:
HAv+H_2O<=>Ac~-+H_3O~+
we have: △G~0=-RT·In(Kα)
or: △g~0=-k_bT·In(K_α)
where, △g~0=g_(Ac)~0-+g_(H3O)~0+-g_(HAc)~0-g_(H2O)~0, g_j~0 is chemical potential or partial molecule Gibbs free-energy of solute j. According to the Scaled Particle Theory (SPT), the Gibbs free-energy of solute j in a solvent is consists of two parts,the first is called the cavitation free-energy (9_j~h), which is the energy needed to transfer a particle from the vacuum to the solvent, and, the second, the interation free-energy (g_j~(OR)), the dispersion energy (g_j~(DS)) and the static energy (g_j~(EL)), So:
g_i~0=g_j~h+g_j~(IN)+g_j~(OR)+g_j~(DS)+g_j~(EL)
then we have: K_a/k_a~0=exp(-Δg~0/k_bT)
where K_a is the ionization constant of HAc in the vacuum, and, is unknown. To solve the problem, we have to select another standard solvent in which, the K_a′ of HAc is well known of course, water is the best one, in it, the K_a′ of HAc is 1.754×10~(-5) at 298 K, and finally we have
K_a=K_a′exp(-Δ(Δg~0/k_bT)
where: Δ(Δg~0)=Δg~0 (in the solvent studying)-Δg~0′ (in water)
According to the theory and formula developed above, we took a series of MeOH-Water mixtures and 1,4-Dioxane-Water mixtures as example in this article, and calculated the K_a of HAc in those mixtures. By comparing the values with that from literatures we found that they are accordance well when the weight per-cent of the non-water conponents is less than 90% and not as larger than 90%. The reasons causing the results are discussed mainly at the end.
Using a precision static oxygen-bomb calorimeter, the standard energies of combustion at 298.15 K of tetra-(o-methoxyphenyl)porphyrin and tetra-(p-dimethylaminophenyl) porphyrin were determined to be-32. 7967±0.0122 kJ g~(-1), -34.5011±0.0115 kJ g~(-1) respectively, the corresponding standard enthalpies of formation at 298.15K were calculated to be -205.8±9.0 kJ mol~(-1), -434.8±9.1 kJ mol~(-1).
In this paper, the kinectics and quantum yields of heteropolyanion P_2Mo_(18)O_(62)~(6-) excitation state reduced by methanol, ethanol, n-propanol, 2-propanol, ethylene glycol, and tert-butyl alcohol are reported.
We have measured the conversion rate of HPC to its reduced form HPB under the irradiation of Xe lamp when mixed with aliphatic alcohol. By a od linear relation between the concentration of HPB and the reaction time (Figure 2), a zero -order reaction was shown. The quantum yield of HPB was measured in the presence of aliphatic alcohol, the rate constants κ_r defined by d(HPB)/dt=κ_r(HPC*) (Aliphatic alcohol) wwere also estimated. The sequence of the κ_r is as follows:
ethylene glycol>2-propanol>n-propanol~ethanol>methanol>>tert-butyl alcohol
In addition, the spectra and properties of both HPC and HPB have been compared.
The second order rate constants of the reaction between O(~3P) and 3-pentanone were measured over temperature range 313-513K with discharge flow-chemiluminescence technique. The dependence of the rate constant on temperature was determined to be
k=1.41±0.46×10~(-10)exp(-5.76±0.07×10~3/1.987T)cm~8 molecule~(-1) s~(-1).
By dynamic technique, the dependence of adsorption and surface reaction rate coefficients for α-methyl styrene hydrogenation on the properties of active sites of Pd/Al_2O_3 catalyst was studied. The results showed that there were two kinds of active sites on the surface of Pd/Al_O_3. Their number N_t, active frequency AF and the number of active atoms in an active site m were obtained and their variations were also studied. The coefficients of adsorption equilibrium, overall reaction rate and adsorption and surface reaction rate coefficients for a single active site κ~*, κ_0~*, κ_0~* and κ_r were calculated. Their changes with Pd content were as same as that of active frequency AF except for κ_r and the change of κ_r was consistent with that of m value. In summary, the kinetic parameters of a catalytic reaction depend not only on the number of active sites, but also on some properties of the active site, such as AF and m value.
