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1988 Volume 4 Issue 3
1988, 4(03): 225-228
doi: 10.3866/PKU.WHXB19880301
Abstract:
Photofragmentation of CH_3SSCH_3 at 248nm was studied by using rotatable pulsed molecular beam crossed with excimer laser beam. TOF spectra of the photofragments were measured at eight different lab angles. The energy partitioning between the internal and translational freedoms in CH_3S fragments showed that the dissociation of S—S bond in CH_3SSCH_3 is consistent with impulsive dynamic model. The S—S bond energy in CH_3SSCH_3 was estimated to be 263±11 kJ mol~(-1) based on the maximum translational energy release in CH_3S fragments. The fact that the C—S bond dissociation at 248 nm was not observed in this work may indicate the intramolecular energy transfer is not fast enough comparing with S—S bond scission and suggest that the bond angle between S—S and C—S bond should be close to 90°, instead of linear structure of CSSC frame. The observation of the wide peak in TOF spectra of CH_3S fragments was explained due to the photodissociation of dimer (CH_3SSCH_3)_2, which was formaed in the supersonic molecular beam.
Photofragmentation of CH_3SSCH_3 at 248nm was studied by using rotatable pulsed molecular beam crossed with excimer laser beam. TOF spectra of the photofragments were measured at eight different lab angles. The energy partitioning between the internal and translational freedoms in CH_3S fragments showed that the dissociation of S—S bond in CH_3SSCH_3 is consistent with impulsive dynamic model. The S—S bond energy in CH_3SSCH_3 was estimated to be 263±11 kJ mol~(-1) based on the maximum translational energy release in CH_3S fragments. The fact that the C—S bond dissociation at 248 nm was not observed in this work may indicate the intramolecular energy transfer is not fast enough comparing with S—S bond scission and suggest that the bond angle between S—S and C—S bond should be close to 90°, instead of linear structure of CSSC frame. The observation of the wide peak in TOF spectra of CH_3S fragments was explained due to the photodissociation of dimer (CH_3SSCH_3)_2, which was formaed in the supersonic molecular beam.
1988, 4(03): 229-233
doi: 10.3866/PKU.WHXB19880302
Abstract:
Studies on high-T_c superconductor Ba_2YCu_3O_(6.92) using thermogravimetry, temperature programmed decomposition, oxygen isotopic exchange method are reported. There are six steps in the thermogavimetric graph of Ba_2YCu_3O_(6.92). At the first step, 0.40 oxygen atom per unit cell is released, the amount of which corresponds to that of the oxygen released from the CuO_4 square plane when the oxidation number of copper reduced from +3 to +2. This amount of oxygen plays a key role on the influence on the T_c of superconductor. At the is 0.45, corresponding to the amount of oxygen released from CuO_4 when the oxidation number of copper changed from +2 to +1. The oxygen atom released totally at the last three steps is 1.07 per unit cell, which correspondes to the oxygen released from CuO_5 square pyramid when the oxidation number of copper changed from +2 to +1. The first three steps are almost continuous, so in TPD curve there is only one peak at 514 ℃ with respect to the three steps in TG curve and the decomposition heat of this one is 171±8 kJ mol~(-1). Another peak which is over 900 ℃ on TPD curve is the result of the loss of oxygen from the last three steps in TG curve. The sample released oxygen can recover its supeconductivity after reabsorbing oxygen. Oxygen isotopic exchange method shows that the oxygen atoms of CuO_4 and CuO_5 groups can be interexchanged under certain temperature and indicates that there is some bonding between CuO_4 square plane and CuO_5 square pyramidal groups in the crystal lattice of Ba_2YCu_3O_(6.92).
Studies on high-T_c superconductor Ba_2YCu_3O_(6.92) using thermogravimetry, temperature programmed decomposition, oxygen isotopic exchange method are reported. There are six steps in the thermogavimetric graph of Ba_2YCu_3O_(6.92). At the first step, 0.40 oxygen atom per unit cell is released, the amount of which corresponds to that of the oxygen released from the CuO_4 square plane when the oxidation number of copper reduced from +3 to +2. This amount of oxygen plays a key role on the influence on the T_c of superconductor. At the is 0.45, corresponding to the amount of oxygen released from CuO_4 when the oxidation number of copper changed from +2 to +1. The oxygen atom released totally at the last three steps is 1.07 per unit cell, which correspondes to the oxygen released from CuO_5 square pyramid when the oxidation number of copper changed from +2 to +1. The first three steps are almost continuous, so in TPD curve there is only one peak at 514 ℃ with respect to the three steps in TG curve and the decomposition heat of this one is 171±8 kJ mol~(-1). Another peak which is over 900 ℃ on TPD curve is the result of the loss of oxygen from the last three steps in TG curve. The sample released oxygen can recover its supeconductivity after reabsorbing oxygen. Oxygen isotopic exchange method shows that the oxygen atoms of CuO_4 and CuO_5 groups can be interexchanged under certain temperature and indicates that there is some bonding between CuO_4 square plane and CuO_5 square pyramidal groups in the crystal lattice of Ba_2YCu_3O_(6.92).
1988, 4(03): 234-238
doi: 10.3866/PKU.WHXB19880303
Abstract:
The Y-Ba-Cu mixed oxide system is obtained when any kinds of materials containing Y, Ba, Cu are heated at 850 ℃. when heated to 900 ℃, an oxygen-rich tetra nal phase I (YBa_2Cu_3O_(6.9)) is formed. At 930 ℃, an oxygen-deficient tetra nal phase Ⅱ (YBa_2Cu_3O_6) appears, and the oxygens at positions (1/2, 0,0) and (0,1/2,0) are almost drived out. The oxygen absorbed above 650 ℃ are equally distributed onto (1/2,0,0) and (0,1/2,0), the amount of which varies with temperature. It is absorbed oxygen that migrates easily from (0, 1/2, 0) to (1/2, 0, 0) as the tetra nal phase transits into the orthorhombic phase at 650 ℃, which makes differences in oxygen-ocupancy at these two positions, such that the structure deviates from tetra nality and the superconduting properties are improved.
The Y-Ba-Cu mixed oxide system is obtained when any kinds of materials containing Y, Ba, Cu are heated at 850 ℃. when heated to 900 ℃, an oxygen-rich tetra nal phase I (YBa_2Cu_3O_(6.9)) is formed. At 930 ℃, an oxygen-deficient tetra nal phase Ⅱ (YBa_2Cu_3O_6) appears, and the oxygens at positions (1/2, 0,0) and (0,1/2,0) are almost drived out. The oxygen absorbed above 650 ℃ are equally distributed onto (1/2,0,0) and (0,1/2,0), the amount of which varies with temperature. It is absorbed oxygen that migrates easily from (0, 1/2, 0) to (1/2, 0, 0) as the tetra nal phase transits into the orthorhombic phase at 650 ℃, which makes differences in oxygen-ocupancy at these two positions, such that the structure deviates from tetra nality and the superconduting properties are improved.
1988, 4(03): 239-243
doi: 10.3866/PKU.WHXB19880304
Abstract:
A stable orthorhombic superconduting phase LaBa_2Cu_3O_(7-δ), with T_c 82K and Meissner effect 13.6%, has been prepared by citric acid complexation with nitrates. It is determined to be an orderly three layer Ba-La-Ba, oxygen-deficient perovskite structure by X-ray powder diffraction and atomic valence calculation. Through high temperature XRD and DTA-TG study,the phase transition of orthorhombic into tetra nal structure is found to be reversible, and occurs at 450 ℃, not the value 350 ℃ proposed by A. Maeda et al. The superconduting properties are improved as the responsible orthorhombic structure deviates more from tetra nality.
A stable orthorhombic superconduting phase LaBa_2Cu_3O_(7-δ), with T_c 82K and Meissner effect 13.6%, has been prepared by citric acid complexation with nitrates. It is determined to be an orderly three layer Ba-La-Ba, oxygen-deficient perovskite structure by X-ray powder diffraction and atomic valence calculation. Through high temperature XRD and DTA-TG study,the phase transition of orthorhombic into tetra nal structure is found to be reversible, and occurs at 450 ℃, not the value 350 ℃ proposed by A. Maeda et al. The superconduting properties are improved as the responsible orthorhombic structure deviates more from tetra nality.
1988, 4(03): 244-249
doi: 10.3866/PKU.WHXB19880305
Abstract:
The influences (Dilution Shift Effect) of sample concentration on ~1H NMR spectra and spin-lattice relaxation times in benzo-azacrown-ether (CE) -CDCl_3 solutions were discussed in this paper. It was considered that the formation of hydrogen bond complex between CE and CDCl_3 is not the major cause leading to Dilution Shift Effect. Based on experiments, a reaction mechanism for CE in CDCl_3-“tertiary amine-tertiary amino salt exchange” was proposed, which has successfully explained the Dilution Shift Effect. The equilibrium constants K_2[(2.2±0.4)×10~(-2) mol L~(-1), (1.9±0.4)×10~(-2) mol L~(-1) and (1.3±0.4)×10~(-2) mol L~(-1) respectively] and exchange rate constants k[4500±1000 s~(-1), 15000±3000 s~(-1) and 6000±1500 s~(-1) respectively] for this mechanism of “tertiary amine-tertiary amino salt exchange” of I, II and III (see experimental section) were obtained through simulation of chemical shift and line shape of ~1H NMR spectra of CE in CDCl_3. Also, the effects of substitute groups of α—C to N on the Dilution Shift Effect were discussed.
The influences (Dilution Shift Effect) of sample concentration on ~1H NMR spectra and spin-lattice relaxation times in benzo-azacrown-ether (CE) -CDCl_3 solutions were discussed in this paper. It was considered that the formation of hydrogen bond complex between CE and CDCl_3 is not the major cause leading to Dilution Shift Effect. Based on experiments, a reaction mechanism for CE in CDCl_3-“tertiary amine-tertiary amino salt exchange” was proposed, which has successfully explained the Dilution Shift Effect. The equilibrium constants K_2[(2.2±0.4)×10~(-2) mol L~(-1), (1.9±0.4)×10~(-2) mol L~(-1) and (1.3±0.4)×10~(-2) mol L~(-1) respectively] and exchange rate constants k[4500±1000 s~(-1), 15000±3000 s~(-1) and 6000±1500 s~(-1) respectively] for this mechanism of “tertiary amine-tertiary amino salt exchange” of I, II and III (see experimental section) were obtained through simulation of chemical shift and line shape of ~1H NMR spectra of CE in CDCl_3. Also, the effects of substitute groups of α—C to N on the Dilution Shift Effect were discussed.
1988, 4(03): 250-255
doi: 10.3866/PKU.WHXB19880306
Abstract:
Adsorption and desorption of benzene, cyclohexane, n-pentane and n-hexane on four native charcoals were measured. The adsorption behavior of the charcoals was interpreted with respect to the specific pore volume and pore size distribution by the ~1H NMR parameters measured, which showed that capillary condensation takes place in the micropores with radius less than 3.0 nm. The degree of high field shift of the adsorbed hydrocarbons gives a measure of the ratio between specific surface and specific pore volume, which may influence the adsorption capacity of the charcoal. Spin lattice relaxation time of the adsorbed hydrocarbons is independent on their species, but closely related to the total amount of the surface acid groups of the charcoal.
Adsorption and desorption of benzene, cyclohexane, n-pentane and n-hexane on four native charcoals were measured. The adsorption behavior of the charcoals was interpreted with respect to the specific pore volume and pore size distribution by the ~1H NMR parameters measured, which showed that capillary condensation takes place in the micropores with radius less than 3.0 nm. The degree of high field shift of the adsorbed hydrocarbons gives a measure of the ratio between specific surface and specific pore volume, which may influence the adsorption capacity of the charcoal. Spin lattice relaxation time of the adsorbed hydrocarbons is independent on their species, but closely related to the total amount of the surface acid groups of the charcoal.
1988, 4(03): 256-261
doi: 10.3866/PKU.WHXB19880307
Abstract:
The translational and internal energy distributions of the photofragments for the processes C_2H_5I→C_2H_5+I~*(~2p_(1/2)) and C_2H_5I→C_2H_5+I(~2p_(3/2))have been measured by using a rotatable molecular beam and time of flight method. The ratio I~*/I determined is 2.37. The characteristics of the electronic excited state, the origin of the I(~2p_(3/2)) channel and the vibrational excitations in the ethyl radicals are discussed.
The translational and internal energy distributions of the photofragments for the processes C_2H_5I→C_2H_5+I~*(~2p_(1/2)) and C_2H_5I→C_2H_5+I(~2p_(3/2))have been measured by using a rotatable molecular beam and time of flight method. The ratio I~*/I determined is 2.37. The characteristics of the electronic excited state, the origin of the I(~2p_(3/2)) channel and the vibrational excitations in the ethyl radicals are discussed.
1988, 4(03): 262-266
doi: 10.3866/PKU.WHXB19880308
Abstract:
Quadrupole mass spectrometer was used in the transient response technique as an analytical tool. With this technique the adsorptive characteristics of H_2 and CO on the modified Rh/Al_2O_3 catalysts were studied. It is found that a small amount of H_2 or CO was adsorbed irreversibly on the fresh surface of catalysts at 507 K; H_2 and CO are adsorbed on the same surface sites and CO adsorption is somewhat stronger than H_2 adsorption Addition of the potassium salt reduces the amount of adsorption of H_2 or CO, but enhances the difference of adsorption strength between CO and H_2.
Quadrupole mass spectrometer was used in the transient response technique as an analytical tool. With this technique the adsorptive characteristics of H_2 and CO on the modified Rh/Al_2O_3 catalysts were studied. It is found that a small amount of H_2 or CO was adsorbed irreversibly on the fresh surface of catalysts at 507 K; H_2 and CO are adsorbed on the same surface sites and CO adsorption is somewhat stronger than H_2 adsorption Addition of the potassium salt reduces the amount of adsorption of H_2 or CO, but enhances the difference of adsorption strength between CO and H_2.
1988, 4(03): 267-272
doi: 10.3866/PKU.WHXB19880309
Abstract:
The structure and phase content in industrial catalyst NiO/α-Al_2O_3 before and after reaction were studied by EXAFS. Part of NiO in the catalyst is reduced to Ni phase. The reducing amount is different for the samples located at different height of the reactor. The phase contents of NiO and Ni were measured and the local structure around Ni atoms was measured by using mixed phase EXAFS analysis method. The results show that the average coordination number of Ni atom in Ni phase is decreased compared with metal Ni. This is caused by more Ni atoms located at surface state. The dimension of Ni cluster is estimated. Meanwhile there is no obvious change of the environment of Ni atom in NiO phase before and after reaction.
The structure and phase content in industrial catalyst NiO/α-Al_2O_3 before and after reaction were studied by EXAFS. Part of NiO in the catalyst is reduced to Ni phase. The reducing amount is different for the samples located at different height of the reactor. The phase contents of NiO and Ni were measured and the local structure around Ni atoms was measured by using mixed phase EXAFS analysis method. The results show that the average coordination number of Ni atom in Ni phase is decreased compared with metal Ni. This is caused by more Ni atoms located at surface state. The dimension of Ni cluster is estimated. Meanwhile there is no obvious change of the environment of Ni atom in NiO phase before and after reaction.
1988, 4(03): 273-278
doi: 10.3866/PKU.WHXB19880310
Abstract:
The behaviors of powder microelectrodes for irreversible reduction of oxygen and thionyl chloride were studied. The postulation that micro-powder electrode is equivalent to a microelectrode with highly active and extended surface was supported by experimental results. This techniques could be widely applicable to the study of electrochemical behaviors of various powder electro-catalysts and to the construction of microelectrodes with fast-response and sensitivity.
The behaviors of powder microelectrodes for irreversible reduction of oxygen and thionyl chloride were studied. The postulation that micro-powder electrode is equivalent to a microelectrode with highly active and extended surface was supported by experimental results. This techniques could be widely applicable to the study of electrochemical behaviors of various powder electro-catalysts and to the construction of microelectrodes with fast-response and sensitivity.
1988, 4(03): 279-284
doi: 10.3866/PKU.WHXB19880311
Abstract:
~(23)Na~+ chemical shifts of NaBPh_4 in mixed solvents of CH_3OH-CH_3COCH_3, CH_3OH-CH_3CN, DMSO-DMF, DMSO-HCONH_2 were measured. By means of isosolvation point the solvating abilities were compared. Meanwhile the data were treated quantitatively to obtain a geometric equilibrium constant, K~1/n, and the free energy of preferential solvation, △G/n, as outlined by Covington. According to the results, the relative solvating abilities of the solvents were found to be: CH_3OH>CH_3COCH_3>CH_3CN, DMSO=HCONH_2>DMF by iso-solvation point and DMSO>HCONH_2>DMF by ΔG/n.
The order indicates that the solvating ability of one solvent in binary mixture depends not only on its own nature, but also on character of cosolvent and structure of binary mixture.
~(23)Na~+ chemical shifts of NaBPh_4 in mixed solvents of CH_3OH-CH_3COCH_3, CH_3OH-CH_3CN, DMSO-DMF, DMSO-HCONH_2 were measured. By means of isosolvation point the solvating abilities were compared. Meanwhile the data were treated quantitatively to obtain a geometric equilibrium constant, K~1/n, and the free energy of preferential solvation, △G/n, as outlined by Covington. According to the results, the relative solvating abilities of the solvents were found to be: CH_3OH>CH_3COCH_3>CH_3CN, DMSO=HCONH_2>DMF by iso-solvation point and DMSO>HCONH_2>DMF by ΔG/n.
The order indicates that the solvating ability of one solvent in binary mixture depends not only on its own nature, but also on character of cosolvent and structure of binary mixture.
1988, 4(03): 285-289
doi: 10.3866/PKU.WHXB19880312
Abstract:
An improved apparatus for precisely measuring the gas solubilities in mixed solvents was reported. The apparatus can also be used to determine the vapor pressures of solvents. With this apparatus, the solubilities of hydrogen in acetone, water and acetone-water mixed solvents at 20-40 ℃, and corresponding vapor pressures of the mixed solvents were measured. The results were discussed preliminarily.
An improved apparatus for precisely measuring the gas solubilities in mixed solvents was reported. The apparatus can also be used to determine the vapor pressures of solvents. With this apparatus, the solubilities of hydrogen in acetone, water and acetone-water mixed solvents at 20-40 ℃, and corresponding vapor pressures of the mixed solvents were measured. The results were discussed preliminarily.
1988, 4(03): 290-295
doi: 10.3866/PKU.WHXB19880313
Abstract:
The adhesion tensions of surfactant solution/solid interface hare been measured by Wilhelmy method. The adsorptions of surfactants at L/S interface have been calculated from the adhesion tensions by applying Gibbs'equation and Young's equation. This method is preferable to the γ—θ method, since it would be more simple—only one quantity needed to be measured comparing to two quantities needed in γ-θ method, more exact—the concentration of solution would not be changed by adsorption, and better repeatability.[see Tab.1]
The systems composed of the aqueous solutions of C_(12)H_(25)SO_4Na, C_(16)N_(33)N(CH_3)_3Br and C_7F_(15)COONa and the solid of paraffin, polyTatraFluoroEthylene, Methylated Glass and polyMethyl Methacrylate have been investigated. Data of adhesionten sion indicate that the fluorocarbon surfactant will be better for improving the hydrophilicity of polytetrafluoroethylene. Than the hydrocarbon surfactants, and the hrdrocarbon surfactants show more effectiveness in making paraffin and methylated Glass hydrophilic. Here mutualphobicity between fluorocarbon andhydrooarbon chain was revealed once more. The order of saturated adsorptions of various surfactants on solids is Γ_(PTFE)>Γ_(PARAFFIN)>Γ_(M-G)>Γ_(PMMA). It just reverse thes order of the adhesion tensions of water/solid interfaces, which indicates the hydrophobicity of the solids.
The adhesion tensions of surfactant solution/solid interface hare been measured by Wilhelmy method. The adsorptions of surfactants at L/S interface have been calculated from the adhesion tensions by applying Gibbs'equation and Young's equation. This method is preferable to the γ—θ method, since it would be more simple—only one quantity needed to be measured comparing to two quantities needed in γ-θ method, more exact—the concentration of solution would not be changed by adsorption, and better repeatability.[see Tab.1]
The systems composed of the aqueous solutions of C_(12)H_(25)SO_4Na, C_(16)N_(33)N(CH_3)_3Br and C_7F_(15)COONa and the solid of paraffin, polyTatraFluoroEthylene, Methylated Glass and polyMethyl Methacrylate have been investigated. Data of adhesionten sion indicate that the fluorocarbon surfactant will be better for improving the hydrophilicity of polytetrafluoroethylene. Than the hydrocarbon surfactants, and the hrdrocarbon surfactants show more effectiveness in making paraffin and methylated Glass hydrophilic. Here mutualphobicity between fluorocarbon andhydrooarbon chain was revealed once more. The order of saturated adsorptions of various surfactants on solids is Γ_(PTFE)>Γ_(PARAFFIN)>Γ_(M-G)>Γ_(PMMA). It just reverse thes order of the adhesion tensions of water/solid interfaces, which indicates the hydrophobicity of the solids.
1988, 4(03): 296-300
doi: 10.3866/PKU.WHXB19880314
Abstract:
Hyperspherical coordinates are employed in describing collinear triatomic reactive scattering. Close-coupling differential equations are obtained by radial piece-wise semi-adiabatic expansion, and solved by first-order Magnus numerical propagation method with multistep exchange-set and reortho nalization procedures. Applicating to H+H_2 and F+H_2 systems, we obtained od results which are in accordance with results of other method for the same systems.
Hyperspherical coordinates are employed in describing collinear triatomic reactive scattering. Close-coupling differential equations are obtained by radial piece-wise semi-adiabatic expansion, and solved by first-order Magnus numerical propagation method with multistep exchange-set and reortho nalization procedures. Applicating to H+H_2 and F+H_2 systems, we obtained od results which are in accordance with results of other method for the same systems.
1988, 4(03): 301-306
doi: 10.3866/PKU.WHXB19880315
Abstract:
Hydrogen spillover has been studied by means of benzene hydrogenation reaction on Al_2O_3. The spillover hydrogen is produced from a point source of spillover Pt/Al_2O_3. Observing benzene adsorbed on Al_2O_3 by in situ FTIR, it is found that the adsorption is a physisorption which occurs by intereaction between π electrons of benzene and surface OH groups of Al_2O_3. The adsorbed force existing between benzene and OH groups is weak, and can not make adsorbed benzene being in active state. Therefore, the benzene hydrogenation reaction on Al_2O3 containing a point source of spillover Pt/Al_2O3 is mainly an interface reaction.
The infrared spectra following observation benzene hydrogenation reaction illustrate that there are a few cyclohexane molecules in beam after the reaction proceeds for 15 mimutes at 50 ℃ and 550 Torr of H_2, and its intensities of CH_2 stretching vibration bands increase linearly with time until all benzene molecules in beam are transformed after 5 hours. These data imply that the spillover hydrogen may migrate some distance on Al_2O3 surface under experiment conditions, and its migrate velocity is the rate controlling step for benzene hydrogenation.
Cyclohexadiene and cyclohexene are observed in further temperature progra mmed surface reaction-mass spectroscopy (TPSR-MS) on Pt/Al_2O_3 catalyst. The result clearly reveals that some successive steps are involved in the hydrogenation process, i.e., firstly benzene is hydrogenated into cyclohexadiene, and then it is transformed into cyclohexene, finally cyclohexane is formed and desorbed In view of their examinable concentrations are low, it may be considered that all these steps are fast.
Hydrogen spillover has been studied by means of benzene hydrogenation reaction on Al_2O_3. The spillover hydrogen is produced from a point source of spillover Pt/Al_2O_3. Observing benzene adsorbed on Al_2O_3 by in situ FTIR, it is found that the adsorption is a physisorption which occurs by intereaction between π electrons of benzene and surface OH groups of Al_2O_3. The adsorbed force existing between benzene and OH groups is weak, and can not make adsorbed benzene being in active state. Therefore, the benzene hydrogenation reaction on Al_2O3 containing a point source of spillover Pt/Al_2O3 is mainly an interface reaction.
The infrared spectra following observation benzene hydrogenation reaction illustrate that there are a few cyclohexane molecules in beam after the reaction proceeds for 15 mimutes at 50 ℃ and 550 Torr of H_2, and its intensities of CH_2 stretching vibration bands increase linearly with time until all benzene molecules in beam are transformed after 5 hours. These data imply that the spillover hydrogen may migrate some distance on Al_2O3 surface under experiment conditions, and its migrate velocity is the rate controlling step for benzene hydrogenation.
Cyclohexadiene and cyclohexene are observed in further temperature progra mmed surface reaction-mass spectroscopy (TPSR-MS) on Pt/Al_2O_3 catalyst. The result clearly reveals that some successive steps are involved in the hydrogenation process, i.e., firstly benzene is hydrogenated into cyclohexadiene, and then it is transformed into cyclohexene, finally cyclohexane is formed and desorbed In view of their examinable concentrations are low, it may be considered that all these steps are fast.
1988, 4(03): 307-313
doi: 10.3866/PKU.WHXB19880316
Abstract:
This paper is concerned with the kinetics and mechanism for the reaction between tetralin and coumarin. Second order reaction kinetics has been established and the kinetic parameters have been determined at the same time by the kinetic experiments. It was found that the reaction followed a concerted reaction mechanism instead of a radical one.
A mechanism containing two steps with Dialin as a intermediate has been suggested and the disscusion for it has also been given in this paper.
This paper is concerned with the kinetics and mechanism for the reaction between tetralin and coumarin. Second order reaction kinetics has been established and the kinetic parameters have been determined at the same time by the kinetic experiments. It was found that the reaction followed a concerted reaction mechanism instead of a radical one.
A mechanism containing two steps with Dialin as a intermediate has been suggested and the disscusion for it has also been given in this paper.
1988, 4(03): 314-319
doi: 10.3866/PKU.WHXB19880317
Abstract:
A number of cyanine dyes and squarylium dyes have been investigeted. The relations between the photovoltaic effect and the dye structures, the mechanism of charge carriers photogeneration in organic materials have been studied. Marked effects of substitutive groups on the photovoltaic effects of donor-acceptor chromophore dyes were observed. We could find convincing indications that the quantum efficiencies vary regularly as the basicity of donor-heterocycle and the ionic potentials of molecules. Finally, the spectral range of squarylium dyes is discussed.
A number of cyanine dyes and squarylium dyes have been investigeted. The relations between the photovoltaic effect and the dye structures, the mechanism of charge carriers photogeneration in organic materials have been studied. Marked effects of substitutive groups on the photovoltaic effects of donor-acceptor chromophore dyes were observed. We could find convincing indications that the quantum efficiencies vary regularly as the basicity of donor-heterocycle and the ionic potentials of molecules. Finally, the spectral range of squarylium dyes is discussed.
1988, 4(03): 320-324
doi: 10.3866/PKU.WHXB19880318
Abstract:
The phase diagram of a pseudo-binary system Li_2WO_4-MgWO_4 has been investigated by means of DTA and X-ray powder diffraction methods. In Li_2WO_4-MgWO_4 system, a new compound Li_2Mg_2(WO_4)_3 is formed by peritectic reaction a+L<=>x at 1010 ℃. The compound Li_2Mg_2(WO_4)_3 belongs to orthorhombic system with space group Pnam. The lattice parameters at room temperature are a=0.5112, b=1.7612 and c=1.0462 nm. The measured density is D_m=5.48 gcm~(-3), and Z=4.
The new compound Li_2Mg_2(WO_4)_3 is an ionic conductor.
The phase diagram of a pseudo-binary system Li_2WO_4-MgWO_4 has been investigated by means of DTA and X-ray powder diffraction methods. In Li_2WO_4-MgWO_4 system, a new compound Li_2Mg_2(WO_4)_3 is formed by peritectic reaction a+L<=>x at 1010 ℃. The compound Li_2Mg_2(WO_4)_3 belongs to orthorhombic system with space group Pnam. The lattice parameters at room temperature are a=0.5112, b=1.7612 and c=1.0462 nm. The measured density is D_m=5.48 gcm~(-3), and Z=4.
The new compound Li_2Mg_2(WO_4)_3 is an ionic conductor.
1988, 4(03): 325-328
doi: 10.3866/PKU.WHXB19880319
Abstract:
The vibrational distributions of CNX~2Σ~+ have been obtained in photolysis of BrCN at 193 nm. An obvious increase of v″=1 population was found with increasing the collision of CN and BrCN. The populations in the v″=2—5 also appeared after the tens collisions. The case can not be found in photolysis of ClCN. A possible explanation was suggested that the CN radical is excited vibrationally due to a recoil which occurs at the collision of CN X~2Σ~+, v″=0 radical carrying 1.5 eV energy with the heavy molecule BrCN. This is similar to the vibrational excitation of CO at collision with a high speed H atom.
The vibrational distributions of CNX~2Σ~+ have been obtained in photolysis of BrCN at 193 nm. An obvious increase of v″=1 population was found with increasing the collision of CN and BrCN. The populations in the v″=2—5 also appeared after the tens collisions. The case can not be found in photolysis of ClCN. A possible explanation was suggested that the CN radical is excited vibrationally due to a recoil which occurs at the collision of CN X~2Σ~+, v″=0 radical carrying 1.5 eV energy with the heavy molecule BrCN. This is similar to the vibrational excitation of CO at collision with a high speed H atom.
1988, 4(03): 329-331
doi: 10.3866/PKU.WHXB19880320
Abstract:
In this paper, a lernary system of Li_2SO_4-C_2H_5OH-H_2O, saturated with salt, was studied. The modified Rose still was utilized to measure the p-T-x-y data for the system at plateau atmosphere (580 Torr or so). According to the Jaques and Furter's pseudo-binary system model, Wilson, NRTL and modified UNIQAC equations were used to correlate with the vapor-liquid equilibrium data. In the calculation, temperature was varied from low to high with steps of 0.01 ℃, and the formulas of |y_1+y_2-1|<10~(-4) or y_1+y_2-1>0 was used for judging the end of the calculation. The method can save the time for computation. The calculated results fit with experimental data, and the maximal deviations of y and T for the modified Uniquac equation are 0.025 molar fraction and 0.23 ℃. In this system, the solubility of lithium sulfate decreases rapidly with the increase of the concentration of alcohol. It means ethanol has a very hight salt-out capacity for lithium sulfate.
In this paper, a lernary system of Li_2SO_4-C_2H_5OH-H_2O, saturated with salt, was studied. The modified Rose still was utilized to measure the p-T-x-y data for the system at plateau atmosphere (580 Torr or so). According to the Jaques and Furter's pseudo-binary system model, Wilson, NRTL and modified UNIQAC equations were used to correlate with the vapor-liquid equilibrium data. In the calculation, temperature was varied from low to high with steps of 0.01 ℃, and the formulas of |y_1+y_2-1|<10~(-4) or y_1+y_2-1>0 was used for judging the end of the calculation. The method can save the time for computation. The calculated results fit with experimental data, and the maximal deviations of y and T for the modified Uniquac equation are 0.025 molar fraction and 0.23 ℃. In this system, the solubility of lithium sulfate decreases rapidly with the increase of the concentration of alcohol. It means ethanol has a very hight salt-out capacity for lithium sulfate.
1988, 4(03): 332-336
doi: 10.3866/PKU.WHXB19880321
Abstract:
The kinetic behavior of reduction for iron (III) oxides was studied by means of TG-DTA thermal analyzer under temperature programed and isothermal conditions with Hydrogen as the reducing gas. The main results show that:
(I) using single kinetic model to fit the overall reductive reactions is impossible. The reduction by hydrogen proceeds in several steps:
Fe_2O3 ~A→Fe_3O_4 ~B→FeO ~C→Fe
It can be treated with different kinetic equations for different periods.
(II) During the first period (including the step A and step B), the main process is nucleation, growth and transformation of Fe_3O_4; the Erofeev equation is better than the Contracting Sphere Model. During the second period (Step C), the main process is reduction of FeO, the Cubic Net Model may be satisfied.
(III) The Fe_3O_4 and FeO are formed as intermediates. The transformation of Fe_3O_4 is the controlling step. FeO may react and vanish rapidly at higher temperature.
(IV) The kinetic parameters in different periods were obtained. The machanism of the reaction was proposed and explained in some detail.
The kinetic behavior of reduction for iron (III) oxides was studied by means of TG-DTA thermal analyzer under temperature programed and isothermal conditions with Hydrogen as the reducing gas. The main results show that:
(I) using single kinetic model to fit the overall reductive reactions is impossible. The reduction by hydrogen proceeds in several steps:
Fe_2O3 ~A→Fe_3O_4 ~B→FeO ~C→Fe
It can be treated with different kinetic equations for different periods.
(II) During the first period (including the step A and step B), the main process is nucleation, growth and transformation of Fe_3O_4; the Erofeev equation is better than the Contracting Sphere Model. During the second period (Step C), the main process is reduction of FeO, the Cubic Net Model may be satisfied.
(III) The Fe_3O_4 and FeO are formed as intermediates. The transformation of Fe_3O_4 is the controlling step. FeO may react and vanish rapidly at higher temperature.
(IV) The kinetic parameters in different periods were obtained. The machanism of the reaction was proposed and explained in some detail.
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