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1993 Volume 9 Issue 3
1993, 9(03): 289-292
doi: 10.3866/PKU.WHXB19930301
Abstract:
The photoionization curves for vinychloride and its abundant fragment ions, es-pecially (C_2H_3)~+ and (C_2H_2)~+, have been measured with synchrotron radiation in the photon energy range from 8-20eV on the photochemistry station at HESYRL. The structure of the photoionization efficiency curves(PIE) for(C_2H_3)~+ and (C_2H_2)~+ were firstly exhibited and explained by the vertical ionization potentials in terms of different ionization processes.
The photoionization curves for vinychloride and its abundant fragment ions, es-pecially (C_2H_3)~+ and (C_2H_2)~+, have been measured with synchrotron radiation in the photon energy range from 8-20eV on the photochemistry station at HESYRL. The structure of the photoionization efficiency curves(PIE) for(C_2H_3)~+ and (C_2H_2)~+ were firstly exhibited and explained by the vertical ionization potentials in terms of different ionization processes.
1993, 9(03): 293-294
doi: 10.3866/PKU.WHXB19930302
Abstract:
Aluminum oxide cluster anions with very broad mass range was produced on a home-made apparatus by laser ablation of α-Al_2O_2 in high vacuum. The recorded mass spectrum showes that, as n>5, only the series of the cluster anions with com-ponents of normal oxidation states were observed. Among the series of cluster anions, the anions foming a complete or near complete hexa nal close-packing structural unit have relative higher signal intensities.
Aluminum oxide cluster anions with very broad mass range was produced on a home-made apparatus by laser ablation of α-Al_2O_2 in high vacuum. The recorded mass spectrum showes that, as n>5, only the series of the cluster anions with com-ponents of normal oxidation states were observed. Among the series of cluster anions, the anions foming a complete or near complete hexa nal close-packing structural unit have relative higher signal intensities.
1993, 9(03): 295-298
doi: 10.3866/PKU.WHXB19930303
Abstract:
The energy transfer from triplex dA_(10)·2dT_(10) or duplex dA_(10)·dA_(10) to ethidium bromide in the 10 mmol·L~(-1) phosphate buffer (pH=7.1) has been investigated. The apparent relative fluorescence quantum yield as a function of excitation wavelength is observed, but the increase in quantum yield in case of the triplex is lower than that for the duplex. This result not only provides strong evidence for intercalative binding of ethidium to both duplex and triplex forms of dA_(10) and dT_(10), but also indicates that binding to the triplex form results in substantially smaller energy transfer than binding to the duplex.
The energy transfer from triplex dA_(10)·2dT_(10) or duplex dA_(10)·dA_(10) to ethidium bromide in the 10 mmol·L~(-1) phosphate buffer (pH=7.1) has been investigated. The apparent relative fluorescence quantum yield as a function of excitation wavelength is observed, but the increase in quantum yield in case of the triplex is lower than that for the duplex. This result not only provides strong evidence for intercalative binding of ethidium to both duplex and triplex forms of dA_(10) and dT_(10), but also indicates that binding to the triplex form results in substantially smaller energy transfer than binding to the duplex.
1993, 9(03): 299-301
doi: 10.3866/PKU.WHXB19930304
Abstract:
Binary cluster ions consisted of aluminum and sulfur(Al_nS_m~+, n up to 63, m up to 94) are produced by laser ablation of a mixture of aluminum powder and sulfur powder. It was found that the formed cluster ions have a uniform increment of Al_2 S_3 in the composition. The photodissociation of the mass-selected cluster ions also show a simple dissociation channel by loss of(Al_2S_3)_x (x=1 or 3). The structural features of the cluster ions have been discussed.
Binary cluster ions consisted of aluminum and sulfur(Al_nS_m~+, n up to 63, m up to 94) are produced by laser ablation of a mixture of aluminum powder and sulfur powder. It was found that the formed cluster ions have a uniform increment of Al_2 S_3 in the composition. The photodissociation of the mass-selected cluster ions also show a simple dissociation channel by loss of(Al_2S_3)_x (x=1 or 3). The structural features of the cluster ions have been discussed.
1993, 9(03): 302-304
doi: 10.3866/PKU.WHXB19930305
Abstract:
The effect of thermal treatment on the surface properties of ultrafine amorphous NiB alloy particles has been studied by H_2 chemisorption, X-ray photoelectron spectroscopy and surface area measurments. It is found that when heating temperature is lower than 623 K the amount of H_2 chemisorbed on NiB alloy catalyst increases with increasing temperature due to the aggregation of oxidized boron species existed in the surface layers of NiB alloy particles. However, thermal treatment at temperature higher than 623K results in a remarkable decrease in the H_2 uptake. This is correlated with not only the sintering of NiB alloy particles but also the migration of boron species alloying with nickel atoms from bulk to surface caused by complete crystallization of amorphous NiB alloy catalyst.
The effect of thermal treatment on the surface properties of ultrafine amorphous NiB alloy particles has been studied by H_2 chemisorption, X-ray photoelectron spectroscopy and surface area measurments. It is found that when heating temperature is lower than 623 K the amount of H_2 chemisorbed on NiB alloy catalyst increases with increasing temperature due to the aggregation of oxidized boron species existed in the surface layers of NiB alloy particles. However, thermal treatment at temperature higher than 623K results in a remarkable decrease in the H_2 uptake. This is correlated with not only the sintering of NiB alloy particles but also the migration of boron species alloying with nickel atoms from bulk to surface caused by complete crystallization of amorphous NiB alloy catalyst.
1993, 9(03): 305-310
doi: 10.3866/PKU.WHXB19930306
Abstract:
MINDO/3 molecular orbital theory has been used study the substituent effect for the thermolysis of RNHCH_2CN. The results show that: (1) the thermolysis of RNHCH_2CN in gas phase is a charge transference reaction triggered by the transfering of atom H(5) with negative charge. The activation barrier, may be lowered by electron donating substituents, while the activation barrier may be raised by electron withdrawing substituents; (2) for this reaction catalyzed by group OH-, both the electron donating and withdrawing substituents show positive effect to the activation barrier.
MINDO/3 molecular orbital theory has been used study the substituent effect for the thermolysis of RNHCH_2CN. The results show that: (1) the thermolysis of RNHCH_2CN in gas phase is a charge transference reaction triggered by the transfering of atom H(5) with negative charge. The activation barrier, may be lowered by electron donating substituents, while the activation barrier may be raised by electron withdrawing substituents; (2) for this reaction catalyzed by group OH-, both the electron donating and withdrawing substituents show positive effect to the activation barrier.
1993, 9(03): 311-318
doi: 10.3866/PKU.WHXB19930307
Abstract:
Three methods, dipping of support into an excess of aqueous solution of (NH_4)_3[Fe(C_2O_4)_3]·xH_2O, incipient wetness impregnation of Fe(NO_3)_3 solution and batch adsorption of Fe(AcAc)_3 in toluene were adopted to prepare supported ferric oxide on ZrO_2. Extensive characterization has been done on the physico-chemical properties of the system. The results indicated that monolayer dispersion of the supported component can be realized using the dipping and adsorption methods. It is difficult to obtain a full coverage of FeO_x on ZrO2. In order to get monolayer dispersion, it is importment that the adsorbed particles should be fully washed with pure toluene in adsorption method or the remained solution on the support particles should be carefully removed in dipping method. The monolayer FeO_x, espically the "quasi-isolated" Fe—O polyhedrons are difficultly detected by FTIR-DRS, LRS as well as XRD. TEM and HEED techniques were adopted to further comfirm the observation. The monolayer dispersed Fe~(3+) is at high spin state and located in a site with distorted rhombic symmetry. The monolayer FeO_x on ZrO_2 is easily reduced to ferrous state as compared with the unsupported bulk ferric oxide or even those monolayer FeO_x species on TiO_2(A) and γ-Al_2O_3. However, further reduction of ferrous ion is still difficult. The microcrystal of ferric oxide on ZrO_2 is reduced through an intermediate compound during the reduction process. The results of pulse reaction of 2-C_4H_8 with or without gas oxygen showed that even the monolayer "quasi-isolated" polyhedrons are still effective to catalyse the ODH of the reactant. Different from the bulk ferric oxide, the monolayer catalysts are sensitive to the presence of gas oxygen for the formation of surface residues and CO_x. In addition, the monolayer FeO_x species are not active for the methanation reaction.
Three methods, dipping of support into an excess of aqueous solution of (NH_4)_3[Fe(C_2O_4)_3]·xH_2O, incipient wetness impregnation of Fe(NO_3)_3 solution and batch adsorption of Fe(AcAc)_3 in toluene were adopted to prepare supported ferric oxide on ZrO_2. Extensive characterization has been done on the physico-chemical properties of the system. The results indicated that monolayer dispersion of the supported component can be realized using the dipping and adsorption methods. It is difficult to obtain a full coverage of FeO_x on ZrO2. In order to get monolayer dispersion, it is importment that the adsorbed particles should be fully washed with pure toluene in adsorption method or the remained solution on the support particles should be carefully removed in dipping method. The monolayer FeO_x, espically the "quasi-isolated" Fe—O polyhedrons are difficultly detected by FTIR-DRS, LRS as well as XRD. TEM and HEED techniques were adopted to further comfirm the observation. The monolayer dispersed Fe~(3+) is at high spin state and located in a site with distorted rhombic symmetry. The monolayer FeO_x on ZrO_2 is easily reduced to ferrous state as compared with the unsupported bulk ferric oxide or even those monolayer FeO_x species on TiO_2(A) and γ-Al_2O_3. However, further reduction of ferrous ion is still difficult. The microcrystal of ferric oxide on ZrO_2 is reduced through an intermediate compound during the reduction process. The results of pulse reaction of 2-C_4H_8 with or without gas oxygen showed that even the monolayer "quasi-isolated" polyhedrons are still effective to catalyse the ODH of the reactant. Different from the bulk ferric oxide, the monolayer catalysts are sensitive to the presence of gas oxygen for the formation of surface residues and CO_x. In addition, the monolayer FeO_x species are not active for the methanation reaction.
1993, 9(03): 319-324
doi: 10.3866/PKU.WHXB19930308
Abstract:
The electrochemical oxidation of cinnamyl alcohol proceeds via consecutive reaction, the follow-up reaction is important in the mediatory systems. The reaction rate de-creased with an increase in water content. An increase in acid concentration also accelares the reaction rate. As expected, the increase of reaction temperature shows an enhancement of the reaction rate for aldehyde and acid formation simultaneously.
The electrochemical oxidation of cinnamyl alcohol proceeds via consecutive reaction, the follow-up reaction is important in the mediatory systems. The reaction rate de-creased with an increase in water content. An increase in acid concentration also accelares the reaction rate. As expected, the increase of reaction temperature shows an enhancement of the reaction rate for aldehyde and acid formation simultaneously.
1993, 9(03): 325-330
doi: 10.3866/PKU.WHXB19930309
Abstract:
The thermal stability of amorphous Ni-RE-P (RE=Y, Ce, Sm) alloy has been studied by differential scanning calorimetry (DSC) in this paper. X-ray diffraction (XRD) and scanning electron microscope(SEM) were used to examine the structure change of the samples heated at different temperatures. The results showed that a small amount of rare earth elements(Y, Ce, Sm) added into amorphous Ni-P alloy could considerably enhanced the thermal stability of amorphous Ni-RE-P alloy. For example, only one exothermic peak appeared at 629 K for Ni-P, while the temperature of maximum exothermic peak which was regarded as crystallization of amorphous Ni-Y-P, Ni-Ce-P and Ni-Sm-P alloys was at 786 K, 795 K and 742 K respectively. With increasing of the treatment temperature, the amorphous Ni-P and Ni-RE-P alloys were progressively crystallized to be simultaneous with presentation of the fine crystals Ni and Ni_3P and the fine crystals grew up to greater crystalline particles due to aggregation of them in the bulk.
It was showed that the value of activation energy of the crystallization of Ni-RE-P was much greater than that of Ni-P, this indicated that the crystallization of Ni-RE-P was more difficult than that of Ni-P. A small amount of rare earth element (Y, Ce, Sm) played an important role in enhancing the thermal stability of amorphous Ni-RE-P alloy.
The thermal stability of amorphous Ni-RE-P (RE=Y, Ce, Sm) alloy has been studied by differential scanning calorimetry (DSC) in this paper. X-ray diffraction (XRD) and scanning electron microscope(SEM) were used to examine the structure change of the samples heated at different temperatures. The results showed that a small amount of rare earth elements(Y, Ce, Sm) added into amorphous Ni-P alloy could considerably enhanced the thermal stability of amorphous Ni-RE-P alloy. For example, only one exothermic peak appeared at 629 K for Ni-P, while the temperature of maximum exothermic peak which was regarded as crystallization of amorphous Ni-Y-P, Ni-Ce-P and Ni-Sm-P alloys was at 786 K, 795 K and 742 K respectively. With increasing of the treatment temperature, the amorphous Ni-P and Ni-RE-P alloys were progressively crystallized to be simultaneous with presentation of the fine crystals Ni and Ni_3P and the fine crystals grew up to greater crystalline particles due to aggregation of them in the bulk.
It was showed that the value of activation energy of the crystallization of Ni-RE-P was much greater than that of Ni-P, this indicated that the crystallization of Ni-RE-P was more difficult than that of Ni-P. A small amount of rare earth element (Y, Ce, Sm) played an important role in enhancing the thermal stability of amorphous Ni-RE-P alloy.
1993, 9(03): 331-335
doi: 10.3866/PKU.WHXB19930310
Abstract:
The electronic structures and redox behavours of the electron donor-acceptor compounds, cyanoethenyl aniline derivatives are investigated by MNDO method in this paper. The frontier orbitals of the compounds result from the interaction between the donor frontier orbital and that of the acceptor. The common oxidizing peaks of these compounds are due to the losing of an electron in N atom of the donor-amino, and the common reducing peaks are brought about by the obtaining of an electron at antibonding orbital of the acceptor-ethenyl. The space effect of the two CH_3 group makes DCEDMA forming a quasi-reversible single electron process. An intermediate stable tert-radical TCEA~(-·) may constitute its redox process.
The electronic structures and redox behavours of the electron donor-acceptor compounds, cyanoethenyl aniline derivatives are investigated by MNDO method in this paper. The frontier orbitals of the compounds result from the interaction between the donor frontier orbital and that of the acceptor. The common oxidizing peaks of these compounds are due to the losing of an electron in N atom of the donor-amino, and the common reducing peaks are brought about by the obtaining of an electron at antibonding orbital of the acceptor-ethenyl. The space effect of the two CH_3 group makes DCEDMA forming a quasi-reversible single electron process. An intermediate stable tert-radical TCEA~(-·) may constitute its redox process.
1993, 9(03): 336-344
doi: 10.3866/PKU.WHXB19930311
Abstract:
Hydroxy-Fe-Al Pillared Clays (FeAl-PILC)containing mixed-metal complexes with various Fe/Al ratios were characterized by UV-DRS, Mossbauer spectrascopy, XPS, TPR measurement. The surface hydroxyl and acidity were determined by IR, Py-IR and TPD. The results have shown that iron in the pillars relatively stronger interacts with alumina in the pillars than with silica of interlayer. The interaction is stronger in FeAl-PILC with Fe/Al ratio<0.5 than that with Fo/Al ratio>0.5. The surface acidity is decreased with increasing of Fe/Al ratio.
Hydroxy-Fe-Al Pillared Clays (FeAl-PILC)containing mixed-metal complexes with various Fe/Al ratios were characterized by UV-DRS, Mossbauer spectrascopy, XPS, TPR measurement. The surface hydroxyl and acidity were determined by IR, Py-IR and TPD. The results have shown that iron in the pillars relatively stronger interacts with alumina in the pillars than with silica of interlayer. The interaction is stronger in FeAl-PILC with Fe/Al ratio<0.5 than that with Fo/Al ratio>0.5. The surface acidity is decreased with increasing of Fe/Al ratio.
1993, 9(03): 345-350
doi: 10.3866/PKU.WHXB19930312
Abstract:
According to the effect of pH on the maximum response current im of the poly-aniline uricase electrode, the plot of log im versus pH shows that the catalytic activity of the uricase electrode is only related to the dissociated group in the base form. The results of the scanning electron micrograph indicate that the stability of the uricase electrode is influenced by its preparing method. The uricase electrode formed by electrochemical immobilization has a high stability over 121 days.
According to the effect of pH on the maximum response current im of the poly-aniline uricase electrode, the plot of log im versus pH shows that the catalytic activity of the uricase electrode is only related to the dissociated group in the base form. The results of the scanning electron micrograph indicate that the stability of the uricase electrode is influenced by its preparing method. The uricase electrode formed by electrochemical immobilization has a high stability over 121 days.
1993, 9(03): 351-356
doi: 10.3866/PKU.WHXB19930313
Abstract:
The inner layer entropy of formation of metal/solution interface (△S~(m-d)) as a function of electrode charge (σ) is derived by using statistical mechanics based on the model of dipole orientation distribution presented in previous paper. the relating curves of △S~(m-d) with σ has been calculated for three different interface systems, namely, the Hg/methanol, Hg/ethylene carbonate and Hg/aqueous solution. According to the present results, the variation in △S~(m-d)(σ) of Hg/methnol interface seems to be chiefly depended on the structure of solvate layer and its dipole orientation distribution. But for the interface of the Hg/ethylene carbonate or the Hg/aqueous, the change of ΔS~(m-d) with σ would be regarded as due to the contribution of surface Hg atoms.
The inner layer entropy of formation of metal/solution interface (△S~(m-d)) as a function of electrode charge (σ) is derived by using statistical mechanics based on the model of dipole orientation distribution presented in previous paper. the relating curves of △S~(m-d) with σ has been calculated for three different interface systems, namely, the Hg/methanol, Hg/ethylene carbonate and Hg/aqueous solution. According to the present results, the variation in △S~(m-d)(σ) of Hg/methnol interface seems to be chiefly depended on the structure of solvate layer and its dipole orientation distribution. But for the interface of the Hg/ethylene carbonate or the Hg/aqueous, the change of ΔS~(m-d) with σ would be regarded as due to the contribution of surface Hg atoms.
1993, 9(03): 357-365
doi: 10.3866/PKU.WHXB19930314
Abstract:
The activity coefficients of aqueous LiCl in system LiCl-MgCl_2-H_2O were determined at 25 ℃ in the total ionic strength range from 0.05 to 6.0 mol·kg~(-1) by E.M.F. method using a lithium ion-selective electrode and Ag/AgCl electrode.
The electrode pairs used in present work were prepared in our laboratory and performance tests were carried out. linear near-Nernst response, od reproducibility, stability and selectivity were observed.
The Harned coefficients, Pitzer ternary interaction parameters and Scatchard parameters were evaluated from present measurement by using multiple regression. The whole range of the ionic strengths studied.
The experimental activity coefficients were compared with which calculated by Pitzer equation with known parameters from experimental osmotic coefficients.
The activity coefficients of aqueous LiCl in system LiCl-MgCl_2-H_2O were determined at 25 ℃ in the total ionic strength range from 0.05 to 6.0 mol·kg~(-1) by E.M.F. method using a lithium ion-selective electrode and Ag/AgCl electrode.
The electrode pairs used in present work were prepared in our laboratory and performance tests were carried out. linear near-Nernst response, od reproducibility, stability and selectivity were observed.
The Harned coefficients, Pitzer ternary interaction parameters and Scatchard parameters were evaluated from present measurement by using multiple regression. The whole range of the ionic strengths studied.
The experimental activity coefficients were compared with which calculated by Pitzer equation with known parameters from experimental osmotic coefficients.
1993, 9(03): 366-373
doi: 10.3866/PKU.WHXB19930315
Abstract:
The osmotic coefficients of aqueous mixtures of Li_2SO_4 and MgSO_4 have been measured from 1.4 to 13.5 mol·(kg)~(-1) at 25 ℃ by using the isopiestic method. In the ranges of 0.2—8.7 and 0.6—12.7 mol·(kg)~(-1) the osmotic coefficients of Li_2SO_4 and MgSO_4 were also reported respectively. Ion interaction parameters of Pitzer model and Scatchard model have been calculated from these measurements. In comparison with Mckay-Perring method, the osmotic and activity coefficients for Li_2SO_4-MgSO_4 mixtures are fairly reliably represented by both Pitzer's equation and Scatchard's neutral electrolyte equation. The predicted solubilities for this system using Pitzer's approach show od agreement with experimental results.
The osmotic coefficients of aqueous mixtures of Li_2SO_4 and MgSO_4 have been measured from 1.4 to 13.5 mol·(kg)~(-1) at 25 ℃ by using the isopiestic method. In the ranges of 0.2—8.7 and 0.6—12.7 mol·(kg)~(-1) the osmotic coefficients of Li_2SO_4 and MgSO_4 were also reported respectively. Ion interaction parameters of Pitzer model and Scatchard model have been calculated from these measurements. In comparison with Mckay-Perring method, the osmotic and activity coefficients for Li_2SO_4-MgSO_4 mixtures are fairly reliably represented by both Pitzer's equation and Scatchard's neutral electrolyte equation. The predicted solubilities for this system using Pitzer's approach show od agreement with experimental results.
1993, 9(03): 374-381
doi: 10.3866/PKU.WHXB19930316
Abstract:
The acidic properties of four REUSY zeolites were studied by NH_3-TPD and IR spectra. The results show that the spectra of hydroxyl groups of REUSY are very complicated. It can be distinguished as three kinds of hydroxyl groups i.e. silicon hydroxyl groups, high frequency hydroxyl groups and low frequency hydroxyl groups. The acidic or nonacidic hydroxyl groups can also be seperated by the IR differential spectra. When the acidic properties were related to the distribution of framework silicon and aluminum and extraframework aluminun measured by ~(29)Si and ~(27)Al MAS NMR, and also to the secondary mesopores formed in the process of dealumination, it was found that when (Si/Al)_F is about 3 to 4, the acid sites corresponding to the Si(3Al) or Si(2Al) are mainly removed from the α-cages. As the (Si/Al) decreases with the Si(2Al) are removed from the β-cages and hexa nal cages. The results also show that a portion of framework acidic high frequency hydroxyl groups can not be accessed by pyridine molecules, but the low frequency hydroxyl groups can be accessed by Py molecules due to the formation of secondary mesopores. On dealumination, the Bronsted, Lewis and the total acid sites all decrease, and the strength of strong acid sites and Bronsted acid sites increase.
The acidic properties of four REUSY zeolites were studied by NH_3-TPD and IR spectra. The results show that the spectra of hydroxyl groups of REUSY are very complicated. It can be distinguished as three kinds of hydroxyl groups i.e. silicon hydroxyl groups, high frequency hydroxyl groups and low frequency hydroxyl groups. The acidic or nonacidic hydroxyl groups can also be seperated by the IR differential spectra. When the acidic properties were related to the distribution of framework silicon and aluminum and extraframework aluminun measured by ~(29)Si and ~(27)Al MAS NMR, and also to the secondary mesopores formed in the process of dealumination, it was found that when (Si/Al)_F is about 3 to 4, the acid sites corresponding to the Si(3Al) or Si(2Al) are mainly removed from the α-cages. As the (Si/Al) decreases with the Si(2Al) are removed from the β-cages and hexa nal cages. The results also show that a portion of framework acidic high frequency hydroxyl groups can not be accessed by pyridine molecules, but the low frequency hydroxyl groups can be accessed by Py molecules due to the formation of secondary mesopores. On dealumination, the Bronsted, Lewis and the total acid sites all decrease, and the strength of strong acid sites and Bronsted acid sites increase.
1993, 9(03): 382-385
doi: 10.3866/PKU.WHXB19930317
Abstract:
Single phase perovskite-type oxides,polycrystal powder LaNiO_3 and LaMnO_3, have been prepared by decomposing mixed nitrates and citric acid compexing methods respectively. X-ray powder diffraction analysis showed that the formation of LaNiO_3 was caused by a solid reaction in which mixed oxides were converted into LaNiO_3; while LaMnO_3 was growing out of amorphous substance directly. By DTA, TG and IR etc. measurements, it was found that ion NO_3- took part in the formation of LaNiO_3 and LaMnO_3. At the same time, the function of the complexing agent was discussed. Citric acid favors fomation of single phase pevoskite-type oxides, especially in the case of LaMnO_3.
Single phase perovskite-type oxides,polycrystal powder LaNiO_3 and LaMnO_3, have been prepared by decomposing mixed nitrates and citric acid compexing methods respectively. X-ray powder diffraction analysis showed that the formation of LaNiO_3 was caused by a solid reaction in which mixed oxides were converted into LaNiO_3; while LaMnO_3 was growing out of amorphous substance directly. By DTA, TG and IR etc. measurements, it was found that ion NO_3- took part in the formation of LaNiO_3 and LaMnO_3. At the same time, the function of the complexing agent was discussed. Citric acid favors fomation of single phase pevoskite-type oxides, especially in the case of LaMnO_3.
1993, 9(03): 386-391
doi: 10.3866/PKU.WHXB19930318
Abstract:
Microphotoelectrochemical etching of n-GaAs by focused He-Ne laser was inven-stigated. An etched pattern was scribed on the n-GaAs surface while the sample moved in X-Y two directions by means of two motors controlled by microcomputer. The diameter of the etched holes was 2 μm. The intensity of the laser light, the concen-trations of different etchants, such as KOH, _2SO_4, HCl and KCl etc., the etching time, the electrode potentials effected the diameters and depths of the etched holes. The experiment results were discussed and analyzed in this paper.
Microphotoelectrochemical etching of n-GaAs by focused He-Ne laser was inven-stigated. An etched pattern was scribed on the n-GaAs surface while the sample moved in X-Y two directions by means of two motors controlled by microcomputer. The diameter of the etched holes was 2 μm. The intensity of the laser light, the concen-trations of different etchants, such as KOH, _2SO_4, HCl and KCl etc., the etching time, the electrode potentials effected the diameters and depths of the etched holes. The experiment results were discussed and analyzed in this paper.
1993, 9(03): 392-397
doi: 10.3866/PKU.WHXB19930319
Abstract:
The activity coefficients of chlorobenzene, m-,p-dichlorobenzene and 1,2,4-tri-chlorobenzene in NaCl, KCl, Na_2CO_3, K_2SO_4 and CaCl_2 aqueous salt solutions, and chlorobenzcne in Et_4NBr have been determined at 298.15 K by spectrophotometry.
The chlorobenzene in Et_4NBr aqueous salt solution is salting-in, while others are salting-out. The experimentsl salting-out orders are as follows: K_2SO_4>Na_2Co_3>CaCl_2>NaCl>KCl. These results are compared with the calculated results of Debye-McAulay and Conway-Desnoyers-Smith electrostatic theories; Masterton-Lee scaled particle theory. McDevit-Long internal pressure theory and modified internal pressure theory. It is verified that the modified internal pressure theory coincides with the experimental value better.
The activity coefficients of chlorobenzene, m-,p-dichlorobenzene and 1,2,4-tri-chlorobenzene in NaCl, KCl, Na_2CO_3, K_2SO_4 and CaCl_2 aqueous salt solutions, and chlorobenzcne in Et_4NBr have been determined at 298.15 K by spectrophotometry.
The chlorobenzene in Et_4NBr aqueous salt solution is salting-in, while others are salting-out. The experimentsl salting-out orders are as follows: K_2SO_4>Na_2Co_3>CaCl_2>NaCl>KCl. These results are compared with the calculated results of Debye-McAulay and Conway-Desnoyers-Smith electrostatic theories; Masterton-Lee scaled particle theory. McDevit-Long internal pressure theory and modified internal pressure theory. It is verified that the modified internal pressure theory coincides with the experimental value better.
1993, 9(03): 398-401
doi: 10.3866/PKU.WHXB19930320
Abstract:
We present the measurements of quenching rate constants of CH(A~2△) radical by O_2, cyclo-C_6H_(12) and CS_2 molecules. The time-resolved spectra of emission CH(A~2△-X~2Π) was monitored. The measured quenching rate constants are as follows.
k_q(O_2)=(2.8±0.5)×10~(-11) cm~3·molec~(-1)·s~(-1)
k_q(cyclo-C_6H_(12))=(2.7±0.4)×10~(-10) cm~3·molec~(-1)·s~(-1)
k_q(CS_2)=(4.0±0.6)×10~(-10) cm~3·molec~(-1)·s~(-1)
The value of k_q(O_2) is in od agreement with previous works. The rate constants for quenching by cyclo-C_6H_(12) and CS_2 are reported for the first time.
We present the measurements of quenching rate constants of CH(A~2△) radical by O_2, cyclo-C_6H_(12) and CS_2 molecules. The time-resolved spectra of emission CH(A~2△-X~2Π) was monitored. The measured quenching rate constants are as follows.
k_q(O_2)=(2.8±0.5)×10~(-11) cm~3·molec~(-1)·s~(-1)
k_q(cyclo-C_6H_(12))=(2.7±0.4)×10~(-10) cm~3·molec~(-1)·s~(-1)
k_q(CS_2)=(4.0±0.6)×10~(-10) cm~3·molec~(-1)·s~(-1)
The value of k_q(O_2) is in od agreement with previous works. The rate constants for quenching by cyclo-C_6H_(12) and CS_2 are reported for the first time.
1993, 9(03): 402-405
doi: 10.3866/PKU.WHXB19930321
Abstract:
α-chlorosulfide is one of the important organosulfur compounds. In this article, the structural parameters of α-chloromethylsulfide and its free radical are calculated by ab initio method at STO-3G and 4-31G levels. The Cl-C-S-C dihedral angles of the most stable structures both for the molecule and the free radical are about 60°. However the bond length of C—S bond and C—Cl bond in free radical are shorter than those in molecule. The △E_(cd)~K and △E_(cd)~T are -4.08 and -2.44 kJ·mol~(-1) respectively, it meansec that the electron-donating group, SCH_3, and electron-withdrawing group, Cl, lead to a minute extra stabilization, when they are bearing on the same carbon atom.
α-chlorosulfide is one of the important organosulfur compounds. In this article, the structural parameters of α-chloromethylsulfide and its free radical are calculated by ab initio method at STO-3G and 4-31G levels. The Cl-C-S-C dihedral angles of the most stable structures both for the molecule and the free radical are about 60°. However the bond length of C—S bond and C—Cl bond in free radical are shorter than those in molecule. The △E_(cd)~K and △E_(cd)~T are -4.08 and -2.44 kJ·mol~(-1) respectively, it meansec that the electron-donating group, SCH_3, and electron-withdrawing group, Cl, lead to a minute extra stabilization, when they are bearing on the same carbon atom.
1993, 9(03): 406-410
doi: 10.3866/PKU.WHXB19930322
Abstract:
In order to describe the local close packed structure of various shells near an atom in a simple liquid or a noncrystalline glass, and further study the chemical short-range order, intermediate-range order and the relation between the chemical ordering and the distance, we, in this paper, present the nested Voronoi polyhedron in which the following one includes the preceding one and expound the method of its construction and computation. As an example of application of this method, we report the computation of some configurations of LiCl glass and the statistical analysis of these results.
In order to describe the local close packed structure of various shells near an atom in a simple liquid or a noncrystalline glass, and further study the chemical short-range order, intermediate-range order and the relation between the chemical ordering and the distance, we, in this paper, present the nested Voronoi polyhedron in which the following one includes the preceding one and expound the method of its construction and computation. As an example of application of this method, we report the computation of some configurations of LiCl glass and the statistical analysis of these results.
1993, 9(03): 411-415
doi: 10.3866/PKU.WHXB19930323
Abstract:
This article is a pridiction of the activity coefficients of HCl in a series of MeOH-H_2O, EtOH-H_2O, HAc-H_2O and Dioxane-H_2O mixtures by the mean sphere approximation(MSA). By comparing the results of MSA with those calculated from Pitzer's equation or from literatures in the MeOH-H_2O media, it is shown that the MSA is powerful in the aqueous-nonaqueous media although it takes the diameter of cation as the only adjustable parameter. A disscusion about the results and the diameter of H~+ in each medium is given at the end briefly.
1993, 9(03): 416-420
doi: 10.3866/PKU.WHXB19930324
Abstract:
Thin-layer transmission spectroelectrochemistry provides an in-situ analytical method. Based on previous research, the authors design a new type of thin-layer spectroelectrochemical cell for long optical path length. The construction of the cell is considered to be simplel; it's operation convinent and sensitivity high, it can be widely used. The optical and electrochemical responses of the cell is measured by the ferrocyanide system, it's property is od and reliable.
Thin-layer transmission spectroelectrochemistry provides an in-situ analytical method. Based on previous research, the authors design a new type of thin-layer spectroelectrochemical cell for long optical path length. The construction of the cell is considered to be simplel; it's operation convinent and sensitivity high, it can be widely used. The optical and electrochemical responses of the cell is measured by the ferrocyanide system, it's property is od and reliable.
1993, 9(03): 421-423
doi: 10.3866/PKU.WHXB19930325
Abstract:
Vapour pressures of n-heptaae-n-octane and n-octane-iso-octane(2,2,4-trimethyl-pentane) binary systems have been determined at 20.0 ℃, 39.6 ℃ and 55.0 ℃. These two systems are nearly ideal solutions at lower temperatures. But they show small positive deviation from Raoult's law at higher temperatures.
Vapour pressures of n-heptaae-n-octane and n-octane-iso-octane(2,2,4-trimethyl-pentane) binary systems have been determined at 20.0 ℃, 39.6 ℃ and 55.0 ℃. These two systems are nearly ideal solutions at lower temperatures. But they show small positive deviation from Raoult's law at higher temperatures.
1993, 9(03): 424-432
doi: 10.3866/PKU.WHXB19930326
Abstract:
