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1990 Volume 6 Issue 3
1990, 6(03): 257-258
doi: 10.3866/PKU.WHXB19900301
Abstract:
Negative carbon cluster ions were generated on a conventionally made laser probe time-of-flight mass spectrometer. The mass spectra showed an even/odd alternation of the cluster ion intensities with cluster size up to 12, indicating a chain configuration. For cluster anions larger than 12, the ions containing 4m+1 carbon atoms have higher concentrations in the cluster anion beam, and a cyclic model can explain the observation very well. We therefore conclude that the chain-ring transi-tion occurs at n=12.
Negative carbon cluster ions were generated on a conventionally made laser probe time-of-flight mass spectrometer. The mass spectra showed an even/odd alternation of the cluster ion intensities with cluster size up to 12, indicating a chain configuration. For cluster anions larger than 12, the ions containing 4m+1 carbon atoms have higher concentrations in the cluster anion beam, and a cyclic model can explain the observation very well. We therefore conclude that the chain-ring transi-tion occurs at n=12.
1990, 6(03): 259-262
doi: 10.3866/PKU.WHXB19900302
Abstract:
Subramanian et al. found superconductivity at 80 K in Tl_(0.5)Pb_(0.5)Sr_2CaCu_2O_y sample with YBa_2 Cu_3 O_(7-δ)-like structure. However, there is unstable factor in the structure of the superconductor. Total plus valence is 12.5, and total minus valence is 14. The structure was further stabilized by partial substitution of Y, La, Nd orPr for Ca and Sn~(4+) or Sb~(5+) for (Tl, Pb), so that T_c was achieved above 100 K. For example, T_c is about 103 K in a sample with nominal composition (Tl_(0.4) Pb_(0.5)Sn_(0.2))Sr_2(Ca_(0.8)Y_(0.2))Cu_2O_(7-δ). During the preparation of superconductors, the temperature of samples was very slowly down after sintering, or samples were annealed at 500—700 ℃. The samples absorbed the oxygen during cooling, but no phase change occured. Appropriate amount of the oxygen made T_e higher.
Subramanian et al. found superconductivity at 80 K in Tl_(0.5)Pb_(0.5)Sr_2CaCu_2O_y sample with YBa_2 Cu_3 O_(7-δ)-like structure. However, there is unstable factor in the structure of the superconductor. Total plus valence is 12.5, and total minus valence is 14. The structure was further stabilized by partial substitution of Y, La, Nd orPr for Ca and Sn~(4+) or Sb~(5+) for (Tl, Pb), so that T_c was achieved above 100 K. For example, T_c is about 103 K in a sample with nominal composition (Tl_(0.4) Pb_(0.5)Sn_(0.2))Sr_2(Ca_(0.8)Y_(0.2))Cu_2O_(7-δ). During the preparation of superconductors, the temperature of samples was very slowly down after sintering, or samples were annealed at 500—700 ℃. The samples absorbed the oxygen during cooling, but no phase change occured. Appropriate amount of the oxygen made T_e higher.
1990, 6(03): 263-268
doi: 10.3866/PKU.WHXB19900303
Abstract:
It has been shown that many oxides and salts can disperse spontaneously onto supports with large surface area~[1]. A typical example studied widely is the dispersion of MoO_3 on γ-Al_2O_3. However, the research work about the dispersion mechanism and kinetics is quite few.
Knozinger etc.~[2] suggested that the dispersion of MoO_3 onto the surface of γ-Al_2O_3 may occur through a "gas phase transport" mechanism mainly by assuming an intermediate MoO_2(OH)_2(g), and the presence of water is necessary. Their conclusion was based on a fact that after heating a mixture of MoO_3 and γ-Al_2O_3 in the presence of H_2O vapour at 450 ℃, the characteristic peak at 950 cm~(-1) of monolayer dispersed MoO_3 in Laser Raman Spectrum (in situ) appears, but after heating the mixture in dry oxygen, it can not be observed...
It has been shown that many oxides and salts can disperse spontaneously onto supports with large surface area~[1]. A typical example studied widely is the dispersion of MoO_3 on γ-Al_2O_3. However, the research work about the dispersion mechanism and kinetics is quite few.
Knozinger etc.~[2] suggested that the dispersion of MoO_3 onto the surface of γ-Al_2O_3 may occur through a "gas phase transport" mechanism mainly by assuming an intermediate MoO_2(OH)_2(g), and the presence of water is necessary. Their conclusion was based on a fact that after heating a mixture of MoO_3 and γ-Al_2O_3 in the presence of H_2O vapour at 450 ℃, the characteristic peak at 950 cm~(-1) of monolayer dispersed MoO_3 in Laser Raman Spectrum (in situ) appears, but after heating the mixture in dry oxygen, it can not be observed...
1990, 6(03): 269-271
doi: 10.3866/PKU.WHXB19900304
Abstract:
In this work, expressions for concentration and current in steady-state and tran-sient-state experiments are given for microring electrodes. For the electrode reaction O+ne→R, assuming bulk concentration of R c_R~b=0, under steady-state conditions, we have
G_O=G_R=sum from μ=1 to ∞ α_μ integral from n=0 to ∞ f_μ (α)J_0 (αr/r_2) exp (-αz/r_2) dα
where
f_μ(α)=J_μ(α)/α~μ-sum from r=1 to μ (r_1/r_2)~p[1-(r_1/r_2)~2]~(μ-r)/2~(μ-ν)(μ-ν)! J,(αr_1/r_2)/α~ν
G_O=1 - (C_O/C_O~b), G_R=D_RC_R/(D_OC_O~b)
where c_O~b is the bulk concentration of species O. r_2, r_1 are outer and inner radii respectively. The...
In this work, expressions for concentration and current in steady-state and tran-sient-state experiments are given for microring electrodes. For the electrode reaction O+ne→R, assuming bulk concentration of R c_R~b=0, under steady-state conditions, we have
G_O=G_R=sum from μ=1 to ∞ α_μ integral from n=0 to ∞ f_μ (α)J_0 (αr/r_2) exp (-αz/r_2) dα
where
f_μ(α)=J_μ(α)/α~μ-sum from r=1 to μ (r_1/r_2)~p[1-(r_1/r_2)~2]~(μ-r)/2~(μ-ν)(μ-ν)! J,(αr_1/r_2)/α~ν
G_O=1 - (C_O/C_O~b), G_R=D_RC_R/(D_OC_O~b)
where c_O~b is the bulk concentration of species O. r_2, r_1 are outer and inner radii respectively. The...
1990, 6(03): 272-276
doi: 10.3866/PKU.WHXB19900305
Abstract:
The binding energies of transition metal clusters have been measured as functions of cluster size and composition at first time. The following clusters have been studied. They are cobalt, niobium, iron, nickel, vanadium, tantalum and palladium with cluster size up to 20 atoms. The photodissociation measurement showed that the binding energy is roughly constant with different cluster sizes but differs with different cluster compositions. For almost all clusters measured, the primary one-photon fragmentation pathway is always found to be loss of a single metal from the cluster.
The binding energies of transition metal clusters have been measured as functions of cluster size and composition at first time. The following clusters have been studied. They are cobalt, niobium, iron, nickel, vanadium, tantalum and palladium with cluster size up to 20 atoms. The photodissociation measurement showed that the binding energy is roughly constant with different cluster sizes but differs with different cluster compositions. For almost all clusters measured, the primary one-photon fragmentation pathway is always found to be loss of a single metal from the cluster.
1990, 6(03): 277-282
doi: 10.3866/PKU.WHXB19900306
Abstract:
In the crystal of title complex, the orientation of trithiophene is disorderdered. The determination of the crystal structure of trithiophene TCNQ complex is performed with direct method and trial and error by combining molecular mechanics and computer graphic technique.
The configuration of trithiophene is chosen reasonably with molecular mechanics. And then, the atomic coordinate parameters is transformed into crystal coordinate system with computer graphic techinque. The calculated structural factors are fitted with the experimental factors. The structure is refined by using blocked cascade least-squares refinement. In addition, the packing analysis and the calculation of packing energy of the title complex are performed with OPEC program. The results explain clearly that the orientation disorder of trithiophene in the stack of title complex is favourable for energy.
In the crystal of title complex, the orientation of trithiophene is disorderdered. The determination of the crystal structure of trithiophene TCNQ complex is performed with direct method and trial and error by combining molecular mechanics and computer graphic technique.
The configuration of trithiophene is chosen reasonably with molecular mechanics. And then, the atomic coordinate parameters is transformed into crystal coordinate system with computer graphic techinque. The calculated structural factors are fitted with the experimental factors. The structure is refined by using blocked cascade least-squares refinement. In addition, the packing analysis and the calculation of packing energy of the title complex are performed with OPEC program. The results explain clearly that the orientation disorder of trithiophene in the stack of title complex is favourable for energy.
1990, 6(03): 283-289
doi: 10.3866/PKU.WHXB19900307
Abstract:
The mass balance model of daul retention mechanism in RP-HPLC is established based on the theory of mass transfer. The first moment and the second, third central moments are derived. The total capacity factor k' and HETP in daul retentio-mechanism can be expressed as:
k′=k′_1+k′_2
H=(2γD_m)/μ+2λa_o+{k[k_0+(1+k_0)(k'_1+k'_2)]~2d~(5/3)_pu~(2/3)}/{(1+k_0)~2(1+k'_1+k'_2)~2D~(2/3)_m}
+{θ[k_0+(1+k_0)(k'_1+k'_2)]~2d_pu}{30D_mk_0(1+k_0)~2(1+k'_1+k'_2)~2}+(2u)/{((1+k_0)(1+k'_1+k'_2)~2}(k'_1/k_(d1)+k'_2/k_(d2))
The effects of chromatographic parameters on column efficiency and peak shape are discussed. The approaches to increase column efficiency and eliminate the tail of chromatogram are explained.
The mass balance model of daul retention mechanism in RP-HPLC is established based on the theory of mass transfer. The first moment and the second, third central moments are derived. The total capacity factor k' and HETP in daul retentio-mechanism can be expressed as:
k′=k′_1+k′_2
H=(2γD_m)/μ+2λa_o+{k[k_0+(1+k_0)(k'_1+k'_2)]~2d~(5/3)_pu~(2/3)}/{(1+k_0)~2(1+k'_1+k'_2)~2D~(2/3)_m}
+{θ[k_0+(1+k_0)(k'_1+k'_2)]~2d_pu}{30D_mk_0(1+k_0)~2(1+k'_1+k'_2)~2}+(2u)/{((1+k_0)(1+k'_1+k'_2)~2}(k'_1/k_(d1)+k'_2/k_(d2))
The effects of chromatographic parameters on column efficiency and peak shape are discussed. The approaches to increase column efficiency and eliminate the tail of chromatogram are explained.
1990, 6(03): 290-297
doi: 10.3866/PKU.WHXB19900308
Abstract:
Crystalline MoO_3 and supports NaY, mordenite are mixed thoroughly, and the mixtures are calcined at 450 ℃ for 24 hours. A series of zeolites with dispersed MoO_3 are studied by XRD, Laser Raman, IR spectroscopy and surface area measurements. It is shown that duriag the calcination MoO_3 interacts strongly with NaY and mordenite. As a result of this sarface interaction MoO_3 migrates into the cavities of zeolites and disperses on it's surface as a non-crystalline layer. Moreover, the framework of NaY is destroyed by the dispersed MoO_3, but there are less effects on the mordenite's structure because of it's higher stability.
By XRD method, we estimate the maximum amount of dispersed MoO_3 is 0.54 and 0.11 gram per gram of NaY and mordenite respectively.
Crystalline MoO_3 and supports NaY, mordenite are mixed thoroughly, and the mixtures are calcined at 450 ℃ for 24 hours. A series of zeolites with dispersed MoO_3 are studied by XRD, Laser Raman, IR spectroscopy and surface area measurements. It is shown that duriag the calcination MoO_3 interacts strongly with NaY and mordenite. As a result of this sarface interaction MoO_3 migrates into the cavities of zeolites and disperses on it's surface as a non-crystalline layer. Moreover, the framework of NaY is destroyed by the dispersed MoO_3, but there are less effects on the mordenite's structure because of it's higher stability.
By XRD method, we estimate the maximum amount of dispersed MoO_3 is 0.54 and 0.11 gram per gram of NaY and mordenite respectively.
1990, 6(03): 298-302
doi: 10.3866/PKU.WHXB19900309
Abstract:
The variations of the G value of the major products (H_2, CH_3CHO, (CH_3CHOH)_2) of the γ-radiolysis of liquid ethanol with the dose absorbed by the ethanol have been measured.
The kineties of α-hydroxyethyl radical reacted with styrene in the ethanol-styrene system has been investigated.
St+CH_3CHOH→P
2CH_3CHOH→(CH_3CHOH)_2
The kinetic equation has been derived as
G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl]
and we t K_6=4.0×10~4 L·mol~(-1)·s~(-1).
The disproportionation of α-hydroxyethyl radical scarcely occurs and acetaldehyde may come from the fast processes in spur.
The variations of the G value of the major products (H_2, CH_3CHO, (CH_3CHOH)_2) of the γ-radiolysis of liquid ethanol with the dose absorbed by the ethanol have been measured.
The kineties of α-hydroxyethyl radical reacted with styrene in the ethanol-styrene system has been investigated.
St+CH_3CHOH→P
2CH_3CHOH→(CH_3CHOH)_2
The kinetic equation has been derived as
G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl]
and we t K_6=4.0×10~4 L·mol~(-1)·s~(-1).
The disproportionation of α-hydroxyethyl radical scarcely occurs and acetaldehyde may come from the fast processes in spur.
1990, 6(03): 303-307
doi: 10.3866/PKU.WHXB19900310
Abstract:
Using potential sweep and potential-time sequence techniques, we have studied the adsorbed intermediates for the electrocatalytic oxidation of tetrahydrofuran on platinum electrode in HClO_4 aqueous solution, in comparison with the analo uselectrochemical behaviours of n-butanol and 1, 4-butanediol. We arrived at the following main conclusions:
(1) Three different intermediates (P_1, P_2 and P_3) form indenendently from tetrahydrofuran on the surface of platinum anode.
(2) The surface hydrogen is neccessary for the formation of all the intermediates, and the free active site is also neccessary for the intermediate P_1.
(3) Probably the ...
Using potential sweep and potential-time sequence techniques, we have studied the adsorbed intermediates for the electrocatalytic oxidation of tetrahydrofuran on platinum electrode in HClO_4 aqueous solution, in comparison with the analo uselectrochemical behaviours of n-butanol and 1, 4-butanediol. We arrived at the following main conclusions:
(1) Three different intermediates (P_1, P_2 and P_3) form indenendently from tetrahydrofuran on the surface of platinum anode.
(2) The surface hydrogen is neccessary for the formation of all the intermediates, and the free active site is also neccessary for the intermediate P_1.
(3) Probably the ...
1990, 6(03): 308-312
doi: 10.3866/PKU.WHXB19900311
Abstract:
The enhancement effect of translational energy of incident molecules on the laser induced gas-surface reactions is studied using a CW supersonic molecular beam technique coupled with time-resolved mass spectrometry. For the visible (560 nm) lasre induced etching reactions of Cl_2 with Ge(111), Si(111) and GaAs(100) surfaces the reaction yields increase obviously with increasing translational energy of incident Cl_2 molecules. There appears to be a translational energy threshold which has a value of 5—7 kJ·mol~(-1) for different etching reactions. Moreover, the dependence of the translational temperatures of the desorbed reaction products on incident translational energy of Cl_2 molecules is investigated by the measured TOF spectra of the products. The results can be explained by the promotion of dissociative chemisorption Cl_2 molecules on semiconductor surface with raising of the incident Cl_2 translational energy.
The enhancement effect of translational energy of incident molecules on the laser induced gas-surface reactions is studied using a CW supersonic molecular beam technique coupled with time-resolved mass spectrometry. For the visible (560 nm) lasre induced etching reactions of Cl_2 with Ge(111), Si(111) and GaAs(100) surfaces the reaction yields increase obviously with increasing translational energy of incident Cl_2 molecules. There appears to be a translational energy threshold which has a value of 5—7 kJ·mol~(-1) for different etching reactions. Moreover, the dependence of the translational temperatures of the desorbed reaction products on incident translational energy of Cl_2 molecules is investigated by the measured TOF spectra of the products. The results can be explained by the promotion of dissociative chemisorption Cl_2 molecules on semiconductor surface with raising of the incident Cl_2 translational energy.
1990, 6(03): 313-317
doi: 10.3866/PKU.WHXB19900312
Abstract:
The transfer of ReO_4~-, IO_4~- and MnO_4~- anions across the water/nitrobenzene interface was investigated by cyctic voltammetry with four electrode system. The transfer process of these anions is ascribed to the diffusion-controlled under the experimental conditions. The linear relationship between the peak current and concentration of these anions in aqueous phase can be used for analysis and monitoring the chemical reaction between IO_4~- and N (C_2H_4OH)_3.
The transfer of ReO_4~-, IO_4~- and MnO_4~- anions across the water/nitrobenzene interface was investigated by cyctic voltammetry with four electrode system. The transfer process of these anions is ascribed to the diffusion-controlled under the experimental conditions. The linear relationship between the peak current and concentration of these anions in aqueous phase can be used for analysis and monitoring the chemical reaction between IO_4~- and N (C_2H_4OH)_3.
1990, 6(03): 318-322
doi: 10.3866/PKU.WHXB19900313
Abstract:
The behaviour of the water on and near the electrode surface in 1.0 mol·dm~(-3) NaF were studied using in-situ FTIR reflection-absorption spectroscopy and cyclic voltammetry. Two mechanisms are proposed to explain the change of water signal in the potential range -0.7 to -0.3 V(vs. SCE)——the change of ordered state of the water molecules near electrode and the formation of adsorbed hydrogen at the cost of the water in the thin layer solution. In the potential range -0.3 to 0.4 V, the orientation of adsorbed OH~- is thought to change from being parallel t perpendicular to the electrode surfacewith in creasing potential. In the range 0.4 to 0.8 V, the slight decrease of water ignal is attributed to thee consum ption of adsorbed OH~- on the formation of Pt-OH on the electrode.
The behaviour of the water on and near the electrode surface in 1.0 mol·dm~(-3) NaF were studied using in-situ FTIR reflection-absorption spectroscopy and cyclic voltammetry. Two mechanisms are proposed to explain the change of water signal in the potential range -0.7 to -0.3 V(vs. SCE)——the change of ordered state of the water molecules near electrode and the formation of adsorbed hydrogen at the cost of the water in the thin layer solution. In the potential range -0.3 to 0.4 V, the orientation of adsorbed OH~- is thought to change from being parallel t perpendicular to the electrode surfacewith in creasing potential. In the range 0.4 to 0.8 V, the slight decrease of water ignal is attributed to thee consum ption of adsorbed OH~- on the formation of Pt-OH on the electrode.
1990, 6(03): 323-328
doi: 10.3866/PKU.WHXB19900314
Abstract:
The adsorption amounts of decylmethylsulfoxide (DEMS) at aqueous solution/carbon black interface and the contact angles of DEMS aqueous solutions on graphite plate have been measured. The influences of temperature, salt (NaCl) and acid(HCl) have been investigated. Typical two plateaux (LS) type adsorption isotherms have been shown. The adsorption ammounts at the first plateau are about 5.7—6.4 μmol·m~(-2) and those at the second one are 42—48 μmol·m~(-2). As the adsorption increasing, the wettability and suspensibility of carbon black in aqueous solution of DEMS were improved obviously. Applying the two-step model of surfactant adsorption on solid/liquid in terface and the general isotherm equation for adsorption of surfactant at solid/liquid in terface (eqn(1))~[5], the experimental results have been interpreted qualitatively and quantitatively.
The adsorption amounts of decylmethylsulfoxide (DEMS) at aqueous solution/carbon black interface and the contact angles of DEMS aqueous solutions on graphite plate have been measured. The influences of temperature, salt (NaCl) and acid(HCl) have been investigated. Typical two plateaux (LS) type adsorption isotherms have been shown. The adsorption ammounts at the first plateau are about 5.7—6.4 μmol·m~(-2) and those at the second one are 42—48 μmol·m~(-2). As the adsorption increasing, the wettability and suspensibility of carbon black in aqueous solution of DEMS were improved obviously. Applying the two-step model of surfactant adsorption on solid/liquid in terface and the general isotherm equation for adsorption of surfactant at solid/liquid in terface (eqn(1))~[5], the experimental results have been interpreted qualitatively and quantitatively.
1990, 6(03): 329-333
doi: 10.3866/PKU.WHXB19900315
Abstract:
According to the fluorescence quenching behaviors and the estimated value of free energy change, as well as the coincidence of the experimental value of ΔG and k_q with the Rehm-Weller's theoretical results, it is inferred that the fluorescence quenching of DCA by campholenic aldehyde is of electron transfer dynamic quenching characteristic.
According to the fluorescence quenching behaviors and the estimated value of free energy change, as well as the coincidence of the experimental value of ΔG and k_q with the Rehm-Weller's theoretical results, it is inferred that the fluorescence quenching of DCA by campholenic aldehyde is of electron transfer dynamic quenching characteristic.
1990, 6(03): 334-340
doi: 10.3866/PKU.WHXB19900316
Abstract:
In this work, the photochemical behaviors of some novel Thioxanthone compounds have been studied. The photochemical problems of these compounds incorporateing with iodonium salts and amine for using as a photosensitive composition have also been investigated. Experimental results indicated that the studied photochemical reactions possess evident character of electron transfer. In addition, the obtained kinetic constants are valuable to understand the suitable region for the application of these photosensitization initiation systems.
In this work, the photochemical behaviors of some novel Thioxanthone compounds have been studied. The photochemical problems of these compounds incorporateing with iodonium salts and amine for using as a photosensitive composition have also been investigated. Experimental results indicated that the studied photochemical reactions possess evident character of electron transfer. In addition, the obtained kinetic constants are valuable to understand the suitable region for the application of these photosensitization initiation systems.
1990, 6(03): 341-346
doi: 10.3866/PKU.WHXB19900317
Abstract:
In acidic or basic buffer solution, nuclear fast red (NFR) exhibits an adsorptive wave. The electrode processes have been verified as an ECE mechanism. The rate constant of the first order chemical reaction following electrochemical reaction has been measured by means of cyclic voltammetry. At pH 4.75, on the surface of mercury electrode, the adsorption of NFR obeys Frumkin isotherm. The adsorption coefficient β= 7.2×10~6 and the interaction factor υ=0.39 have been determined. In the supporting electrolyte containing 0.1 mol·L~(-1) ethylene diamine and 0.3 mol·L~(-1) KCl, at pH 11, the polarographic adsorptive complex wave of RE(III)-NFR has been obtained by using single-sweep polarograph. The electrode processes has been studied.
In acidic or basic buffer solution, nuclear fast red (NFR) exhibits an adsorptive wave. The electrode processes have been verified as an ECE mechanism. The rate constant of the first order chemical reaction following electrochemical reaction has been measured by means of cyclic voltammetry. At pH 4.75, on the surface of mercury electrode, the adsorption of NFR obeys Frumkin isotherm. The adsorption coefficient β= 7.2×10~6 and the interaction factor υ=0.39 have been determined. In the supporting electrolyte containing 0.1 mol·L~(-1) ethylene diamine and 0.3 mol·L~(-1) KCl, at pH 11, the polarographic adsorptive complex wave of RE(III)-NFR has been obtained by using single-sweep polarograph. The electrode processes has been studied.
1990, 6(03): 347-349
doi: 10.3866/PKU.WHXB19900318
Abstract:
The surface dispersion of bifunctional NiO-MoO_3/γ-alumina catalysts prepared by different procedures was studied with Ni-K EXAFS spectroscopy. The contents of NiO(13.6%) and MoO_3(16.5%) were the same in the three samples, which were a little higher than the monolayer dispersion capacity of each component on γ-Al_2O_3. The dispersion temperature was 450 ℃. The sample impregnated with NiO first shows that the NiO is monolayer-dispersed on γ-Al_2O_3 surface and the outer layer is MoO_3. The sample impregnated with MoO_3 and the outer layer is NiO. There is strong interaction between MoO_3 and γ-Al_2O_3 which affects the dispersion of NiO on the surface. The sample impregnated with NiO and MoO_3 simultaneously shows that the Ni is not dispersed in the form of NiO but another compound on the surface.
The surface dispersion of bifunctional NiO-MoO_3/γ-alumina catalysts prepared by different procedures was studied with Ni-K EXAFS spectroscopy. The contents of NiO(13.6%) and MoO_3(16.5%) were the same in the three samples, which were a little higher than the monolayer dispersion capacity of each component on γ-Al_2O_3. The dispersion temperature was 450 ℃. The sample impregnated with NiO first shows that the NiO is monolayer-dispersed on γ-Al_2O_3 surface and the outer layer is MoO_3. The sample impregnated with MoO_3 and the outer layer is NiO. There is strong interaction between MoO_3 and γ-Al_2O_3 which affects the dispersion of NiO on the surface. The sample impregnated with NiO and MoO_3 simultaneously shows that the Ni is not dispersed in the form of NiO but another compound on the surface.
1990, 6(03): 350-353
doi: 10.3866/PKU.WHXB19900319
Abstract:
The theory of the stability of SiO_2 colloid in different electrolyte (NaCl) concen-tration was studied. It was found that the stability of SiO_2 colloidal dispersion was lower with the increase of eletrolyte (NaCl) concentration and the logw-logc relation was straight line. The potential curves in the system were constructed. The stability of SiO_2 colloidal dispersion correspond with the DLVO theory.
The Extrapolation of Rate Constants for Reaction of O(3P) with Ketones Using Transition-State Theory
1990, 6(03): 354-359
doi: 10.3866/PKU.WHXB19900320
Abstract:
Conventional transition-state theory is used for extrapolating rate constant of reactions of O(~3P) atom with ketones to temperature range 200—2000 K. Estimations of structural properties of the activated complex necessary for calculating free energy of activation are presented. Expressions of the rate constant with three parameters are derived. These are as follows (unit: cm~(-3)·molecule~(-1)·s~(-1)).
k=5.34×10~(-20)T~(2.96)exp (-12.4/RT) (for butanone)
k=6.64×10~(-19)T~(2.67)exp (-14.1/RT) (for 3-pentanone)
...
Conventional transition-state theory is used for extrapolating rate constant of reactions of O(~3P) atom with ketones to temperature range 200—2000 K. Estimations of structural properties of the activated complex necessary for calculating free energy of activation are presented. Expressions of the rate constant with three parameters are derived. These are as follows (unit: cm~(-3)·molecule~(-1)·s~(-1)).
k=5.34×10~(-20)T~(2.96)exp (-12.4/RT) (for butanone)
k=6.64×10~(-19)T~(2.67)exp (-14.1/RT) (for 3-pentanone)
...
1990, 6(03): 360-363
doi: 10.3866/PKU.WHXB19900321
Abstract:
A sandwich quartz cell is designed and a flow system is set up for photoacoustic calorimentry measurements in the case of optically thick solutions. Marquardt nonlinear least square is modified to fit the experimental time-resolved waveforms. The quenching of benzophenone triplet state by dienes is observed using the apparatus and the results are in agreement with K. Peters' values.
A sandwich quartz cell is designed and a flow system is set up for photoacoustic calorimentry measurements in the case of optically thick solutions. Marquardt nonlinear least square is modified to fit the experimental time-resolved waveforms. The quenching of benzophenone triplet state by dienes is observed using the apparatus and the results are in agreement with K. Peters' values.
1990, 6(03): 364-370
doi: 10.3866/PKU.WHXB19900322
Abstract:
In this work a modified adsorption method was used to form firstly a saturated Cd or Pb adlayer on platinum single crystal (100) surface, then its surface structure, the electrochemical stability and the desorption-readsorption CV properties were studied. The HCOOH oxidation has been used as a probe to determine the electrocatalytic propertics of Pt (100) with different surface concentration of Cd or Pb adatoms. The results show that Cd adatoms on Pt(100) inhibit both HCOOH dissociation adsorption (to form poisoning intermediates) and HCOOH oxidation via the reactive intermediate, and that Pb adatoms on Pt(100) inhibit only HCOOH disociation adsorption but catalyse HCOOH oxidation via the reactive intermediate, in this case the more Pb adatoms on Pt(100), the higher te catalytic effect. The highest enhanced catalytic effet has been found with the saturated Pb adlayer on Pt(100) (the coverage of Pb, calibrated by hydrogen adsorption, is then equal to 1.0), i.e. with a surface structure of C(2×2)-bridged Pb. The difference of influence to the hydrogen adsorption-desorption process and the different catalytic effect on HCOOH oxidation of Cd and Pb adatoms on Pt(100) were attributed to the intrinsic properties of Cd and Pd elements and also to their interaction with Pt(100). This results indicate that the electrocatalytic mechanism of Cd and Pb adatom on Pt(100) depends on the geometrical surface structure effect and, more importantly, on the electro structure effect during the interaction of adatoms with Pt(100) surface atoms.
In this work a modified adsorption method was used to form firstly a saturated Cd or Pb adlayer on platinum single crystal (100) surface, then its surface structure, the electrochemical stability and the desorption-readsorption CV properties were studied. The HCOOH oxidation has been used as a probe to determine the electrocatalytic propertics of Pt (100) with different surface concentration of Cd or Pb adatoms. The results show that Cd adatoms on Pt(100) inhibit both HCOOH dissociation adsorption (to form poisoning intermediates) and HCOOH oxidation via the reactive intermediate, and that Pb adatoms on Pt(100) inhibit only HCOOH disociation adsorption but catalyse HCOOH oxidation via the reactive intermediate, in this case the more Pb adatoms on Pt(100), the higher te catalytic effect. The highest enhanced catalytic effet has been found with the saturated Pb adlayer on Pt(100) (the coverage of Pb, calibrated by hydrogen adsorption, is then equal to 1.0), i.e. with a surface structure of C(2×2)-bridged Pb. The difference of influence to the hydrogen adsorption-desorption process and the different catalytic effect on HCOOH oxidation of Cd and Pb adatoms on Pt(100) were attributed to the intrinsic properties of Cd and Pd elements and also to their interaction with Pt(100). This results indicate that the electrocatalytic mechanism of Cd and Pb adatom on Pt(100) depends on the geometrical surface structure effect and, more importantly, on the electro structure effect during the interaction of adatoms with Pt(100) surface atoms.
1990, 6(03): 371-374
doi: 10.3866/PKU.WHXB19900323
Abstract:
The CFF method is used on the conformational analysis of the title complex. Eight possible isomers are treated, their minimum energies are given and equilibrium conformations are compared with recent crystal structure determination. Futhermorethe influences of the two five-membered chelate rings on the conformational change of the four-membered ring from puckered form to planar form are discussed in detail and the reproduction of the initia1 stage in the formation of four-membered ring is attempted.
The CFF method is used on the conformational analysis of the title complex. Eight possible isomers are treated, their minimum energies are given and equilibrium conformations are compared with recent crystal structure determination. Futhermorethe influences of the two five-membered chelate rings on the conformational change of the four-membered ring from puckered form to planar form are discussed in detail and the reproduction of the initia1 stage in the formation of four-membered ring is attempted.
1990, 6(03): 375-380
doi: 10.3866/PKU.WHXB19900324
Abstract:
Under single-collision beam-gas scattering conditions the reactions Ba+ C_2H, Br、n-C_3H_7Br、1, 2-C_2H_4Br_2、1,3-C_3H_6Br_2 have been studied using laser induced fluore-scence to detect the BaBr X~2∑~+ product. The vibrational distributions, the fractions of the available energy ing into vibrational and rotational energy of the BaBr products have been calculated by means. of computer simulation. It has been found that the average vibrationel energies of the BaBr products can be described as a linear function of the mass factors for the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br、1,3-C_3H_6Br, and that the potential energy surfaces for these reactions are similar. For the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br, the vibrational increae, but for the reactions Ba+CH_2Br_2、1,2-C_2H_4Br_2、1,3-C_3H_6Br_2, the vibrational excitations of the BaBr products decrease greatly when the number of the carbons increase.
Under single-collision beam-gas scattering conditions the reactions Ba+ C_2H, Br、n-C_3H_7Br、1, 2-C_2H_4Br_2、1,3-C_3H_6Br_2 have been studied using laser induced fluore-scence to detect the BaBr X~2∑~+ product. The vibrational distributions, the fractions of the available energy ing into vibrational and rotational energy of the BaBr products have been calculated by means. of computer simulation. It has been found that the average vibrationel energies of the BaBr products can be described as a linear function of the mass factors for the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br、1,3-C_3H_6Br, and that the potential energy surfaces for these reactions are similar. For the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br, the vibrational increae, but for the reactions Ba+CH_2Br_2、1,2-C_2H_4Br_2、1,3-C_3H_6Br_2, the vibrational excitations of the BaBr products decrease greatly when the number of the carbons increase.
1990, 6(03): 381-382
doi: 10.3866/PKU.WHXB19900325
Abstract:
1990, 6(03): 382-384
doi: 10.3866/PKU.WHXB19900326
Abstract:
