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1993 Volume 9 Issue 4
1993, 9(04): 433-437
doi: 10.3866/PKU.WHXB19930401
Abstract:
The molecular orbitals of the complex Pt(PPh_3)_2-η~2(C_(60)) were investigated via Fenske-Hall molecular orbital calculations on the prototype species Pt(PH_3)_2-η~2C_(60). The results was compared with typical π-complex Pt(PPh_3)_2-η~2C_2H_4. The results of calculation showed that the components of HOMO and LUMO in Pt(PH_3)_2-η~2C_(60) mainly come from C_(60), which is the electron acceptor, but the components of HOMO and LUMO in Pt(PH_3)_2-η~2C_2H_4 molecular orbitals mainly come from Pt(PH_3)_2, which is the electron donor. The ligand C_(60) and C_2H_4 both act as an acceptor, but C_(60) is more stronger than C_2H_4. The LUMO of Pt(PH_3)_2-η~2C_(60) is still situated at lower energy and it is possible to accept further Pt(PH_3)_2 radical on C_(60) surface. From the calculation it was revealed that there are two conjujated chain started on atoms C1 and C6. The Mulliken charge is distributed along these chain alternatively.
The molecular orbitals of the complex Pt(PPh_3)_2-η~2(C_(60)) were investigated via Fenske-Hall molecular orbital calculations on the prototype species Pt(PH_3)_2-η~2C_(60). The results was compared with typical π-complex Pt(PPh_3)_2-η~2C_2H_4. The results of calculation showed that the components of HOMO and LUMO in Pt(PH_3)_2-η~2C_(60) mainly come from C_(60), which is the electron acceptor, but the components of HOMO and LUMO in Pt(PH_3)_2-η~2C_2H_4 molecular orbitals mainly come from Pt(PH_3)_2, which is the electron donor. The ligand C_(60) and C_2H_4 both act as an acceptor, but C_(60) is more stronger than C_2H_4. The LUMO of Pt(PH_3)_2-η~2C_(60) is still situated at lower energy and it is possible to accept further Pt(PH_3)_2 radical on C_(60) surface. From the calculation it was revealed that there are two conjujated chain started on atoms C1 and C6. The Mulliken charge is distributed along these chain alternatively.
1993, 9(04): 438-441
doi: 10.3866/PKU.WHXB19930402
Abstract:
The coefficients b,ρ, and σ in Born-Mayer-Huggins potential were determined empirically for three interactions in CaF_2 system. The potential suggested in this work have reproduced the experimental lattice energy, bulk modulus, and three elastic constant very well. The radial distribution functions for molten calcium fluoride have been given by molecular dynamics simulation with the potential obtained. The results show that there is a great deal of difference in the three radial distribution functions. The first peak of radial distribution function is very sharp in the cation-anion case and smoothing down in the cation-cation and anion-anion case. The maximum of g_(--)(r) distribution is not high and a limp point appears between the first peak and the first valley of g_(--)(r) curve. The distances where the radial distribution function g_(+-)(r) has a maximum are 0.225 nm for T=2000 K and 0.221 nm for T=2200 K. These values are less than 0.2357 nm, the distance between cation and anion in crystalline phase of calcium fluoride, that indicates there are some "holes" and chain-like structures in molten system.
The coefficients b,ρ, and σ in Born-Mayer-Huggins potential were determined empirically for three interactions in CaF_2 system. The potential suggested in this work have reproduced the experimental lattice energy, bulk modulus, and three elastic constant very well. The radial distribution functions for molten calcium fluoride have been given by molecular dynamics simulation with the potential obtained. The results show that there is a great deal of difference in the three radial distribution functions. The first peak of radial distribution function is very sharp in the cation-anion case and smoothing down in the cation-cation and anion-anion case. The maximum of g_(--)(r) distribution is not high and a limp point appears between the first peak and the first valley of g_(--)(r) curve. The distances where the radial distribution function g_(+-)(r) has a maximum are 0.225 nm for T=2000 K and 0.221 nm for T=2200 K. These values are less than 0.2357 nm, the distance between cation and anion in crystalline phase of calcium fluoride, that indicates there are some "holes" and chain-like structures in molten system.
1993, 9(04): 442-446
doi: 10.3866/PKU.WHXB19930403
Abstract:
The collision-free multiphoton ionization of jet cooling CH_3I was studied using a pulsed laser, tunable around 280 and 366 nm with TOF mass spectrometer and mag-netic-bottle TOF photoelectron spectrometer.
MPI of CH_3I in 280 nm region via valence à state can be explained by ladder-switch mechanism according to the following experimental results. The parent ions are almost abscent in the MPI TOF MS. I~+ MPI spectrum gives three resonances corre-sponding to two-photon excitation of I atom at 279.72, 279.25 and 278.50 nm. The I ionic state due to 2+1 REMPI of I atom can be assigned from the REMPI PES.
In 371—365 nm I~+, CH_3~+ and CH_3I~+ were observed in MPI MS. The mass-selected MPI spectra of CH_3I~+ and daughter ion I~+ have similar profiles. In the spectra the two peaks at 365.90 and 369.92 nm are assigned to be two-photon resonance with the Rydberg C state Π(0,0) and Σ(0,0) of CH_3I respectively. The formation of the CH_3I~+ ~2Π_(3/2) and ~2Π_(1/2) state created by 2+1 and 2+2 REMPI resectively were found in PES. REMPI of CH_3I around 366 nm is consistent with the ladder mechanism in which CH_3I is excited into C state upon a two photon absorption and parent ion is formed by the overall 2+1 of 2+2 MPI process. The fragment ions are produced by further dissociation of CH_3I~+ at à state.
The collision-free multiphoton ionization of jet cooling CH_3I was studied using a pulsed laser, tunable around 280 and 366 nm with TOF mass spectrometer and mag-netic-bottle TOF photoelectron spectrometer.
MPI of CH_3I in 280 nm region via valence à state can be explained by ladder-switch mechanism according to the following experimental results. The parent ions are almost abscent in the MPI TOF MS. I~+ MPI spectrum gives three resonances corre-sponding to two-photon excitation of I atom at 279.72, 279.25 and 278.50 nm. The I ionic state due to 2+1 REMPI of I atom can be assigned from the REMPI PES.
In 371—365 nm I~+, CH_3~+ and CH_3I~+ were observed in MPI MS. The mass-selected MPI spectra of CH_3I~+ and daughter ion I~+ have similar profiles. In the spectra the two peaks at 365.90 and 369.92 nm are assigned to be two-photon resonance with the Rydberg C state Π(0,0) and Σ(0,0) of CH_3I respectively. The formation of the CH_3I~+ ~2Π_(3/2) and ~2Π_(1/2) state created by 2+1 and 2+2 REMPI resectively were found in PES. REMPI of CH_3I around 366 nm is consistent with the ladder mechanism in which CH_3I is excited into C state upon a two photon absorption and parent ion is formed by the overall 2+1 of 2+2 MPI process. The fragment ions are produced by further dissociation of CH_3I~+ at à state.
1993, 9(04): 447-449
doi: 10.3866/PKU.WHXB19930404
Abstract:
The vibrationally excited OH(v) from the reaction of O(~1D)+Si(CH_3)_3Cl was observed by UV laser photolysis/FTIR emission spectroscopy. The vibrational number was only up to 3 with a ratio of 1:0.8:0.1 for v=1:2:3. Comparing this result with the similar reaction of O(~1D)+Si(CH_3)_4 which OH(v) vibrational number was high up to 4 with a ratio of 1:1:1:0.3 for v=1:2:3:4 under the same experimental conditions, it was found that the substitution of Cl for CH_3 affected the extent of heavy Si atom blocking the energy migration in a molecule. This results identifies the prediction that the characteristic of electrons in central atom plays an important role in intramolecular energy transfer.
The vibrationally excited OH(v) from the reaction of O(~1D)+Si(CH_3)_3Cl was observed by UV laser photolysis/FTIR emission spectroscopy. The vibrational number was only up to 3 with a ratio of 1:0.8:0.1 for v=1:2:3. Comparing this result with the similar reaction of O(~1D)+Si(CH_3)_4 which OH(v) vibrational number was high up to 4 with a ratio of 1:1:1:0.3 for v=1:2:3:4 under the same experimental conditions, it was found that the substitution of Cl for CH_3 affected the extent of heavy Si atom blocking the energy migration in a molecule. This results identifies the prediction that the characteristic of electrons in central atom plays an important role in intramolecular energy transfer.
1993, 9(04): 450-451
doi: 10.3866/PKU.WHXB19930405
Abstract:
Highly-oriented K(Ta,Nb)O_3 thin film is prepared by Sol-Gel process, using K(OC_2H_5), Nb(OC_2H_5)_5 and Ta(OC_2H_5)_5 as raw materials. The surface of thin film is smooth, homogeneous, crack-free and dense.
1993, 9(04): 452-454
doi: 10.3866/PKU.WHXB19930406
Abstract:
Photolysis of the CHBr_3+O_2 system with the 193 nm laser has been investigated by means of our UV laser photolysis time-resolved infrared spectrometer. CO(v, X~1Σ~+) was observed up to v=10 and population conversion up to v=5. The quenching constants for CO(v=1 to 10) by O_2 have also been deduced. We think that the reaction CHBr_(x)+O_2→CO(v, X~1Σ~+)+other products(x=1 or 2) plays an important role under our experimental conditions.
Photolysis of the CHBr_3+O_2 system with the 193 nm laser has been investigated by means of our UV laser photolysis time-resolved infrared spectrometer. CO(v, X~1Σ~+) was observed up to v=10 and population conversion up to v=5. The quenching constants for CO(v=1 to 10) by O_2 have also been deduced. We think that the reaction CHBr_(x)+O_2→CO(v, X~1Σ~+)+other products(x=1 or 2) plays an important role under our experimental conditions.
1993, 9(04): 455-460
doi: 10.3866/PKU.WHXB19930407
Abstract:
The structure of pillared montmorillonite is partially disordered layer lattice. Its basal spacings can be expanded to many possible values with different probabili-ties depending on the type and structure of the pillars or the preparation conditions. If a formula describing the X-ray diffraction intensity of partially disordered layer lattice as a function of basal spacings and corresponding probabilities is computa-tionally simulated with the experimental XRD pattern, the basal spacings and prob-abilities can thus be obtained. In this work, two of the polyoxyaluminum pillared montmorillonite samples with Al_(13) as main pillars were prepared. The simulated results show that most of the basal spacings are expanded to 1.97 nm with a probability of 0.65 corresponding to Al_(13) as pillars; some of the basal spacings are 1.5 nm with a probability of 0.25 corresponding to Al_6 as the most possible pillaring species; the rest ones are 1.1 nm containing water molecules only in the interlamellar region. The experimental results obtained from CEC, ICP etc. are used to calculate the distribution of the pillars in the interlayer zone. Subsequently, a three-dimensional structural model is built up. The agreement of the pore-volume between theoretical calculation and experimental result verifies the rationality of the structural model. Therefore, the basal spacing usually characterized by d_(001) which is calculated from Bragg equation actually is not exact.
The structure of pillared montmorillonite is partially disordered layer lattice. Its basal spacings can be expanded to many possible values with different probabili-ties depending on the type and structure of the pillars or the preparation conditions. If a formula describing the X-ray diffraction intensity of partially disordered layer lattice as a function of basal spacings and corresponding probabilities is computa-tionally simulated with the experimental XRD pattern, the basal spacings and prob-abilities can thus be obtained. In this work, two of the polyoxyaluminum pillared montmorillonite samples with Al_(13) as main pillars were prepared. The simulated results show that most of the basal spacings are expanded to 1.97 nm with a probability of 0.65 corresponding to Al_(13) as pillars; some of the basal spacings are 1.5 nm with a probability of 0.25 corresponding to Al_6 as the most possible pillaring species; the rest ones are 1.1 nm containing water molecules only in the interlamellar region. The experimental results obtained from CEC, ICP etc. are used to calculate the distribution of the pillars in the interlayer zone. Subsequently, a three-dimensional structural model is built up. The agreement of the pore-volume between theoretical calculation and experimental result verifies the rationality of the structural model. Therefore, the basal spacing usually characterized by d_(001) which is calculated from Bragg equation actually is not exact.
1993, 9(04): 461-465
doi: 10.3866/PKU.WHXB19930408
Abstract:
The micellar aggregation numbers of sodium dodecyl sulfate(SDS), sodium dodecyl sulfonate(AS) and cetyltrimethylammonium bromide(CTAB) has been determined from steady-state fluorescence quenching method, using pyrene(PYR) as probe and diphenyketone(DPK) as quencher. The range of validity of the method used in this work for the determination of micelle aggregation number is discused. The results obtained show that this probe-quencher system applies to the determination of micelle concentrations and aggregation number of anionic and cationic micelles.
The micellar aggregation numbers of sodium dodecyl sulfate(SDS), sodium dodecyl sulfonate(AS) and cetyltrimethylammonium bromide(CTAB) has been determined from steady-state fluorescence quenching method, using pyrene(PYR) as probe and diphenyketone(DPK) as quencher. The range of validity of the method used in this work for the determination of micelle aggregation number is discused. The results obtained show that this probe-quencher system applies to the determination of micelle concentrations and aggregation number of anionic and cationic micelles.
1993, 9(04): 466-472
doi: 10.3866/PKU.WHXB19930409
Abstract:
The monolayers on the water surface were studied by pressure-area isotherms, with five metalloporphyrins and metallophthalocyanines bearing differential substi-tuents. From the limiting areas together with the molecular model, probable orientation of maerocycle in the monolayer and the oriented effect of substituents upon the mac-rocycles were considered. These monolayer were transferred to the substrates by L-B method. The UV-vis spectra of the L-B films and in solution were measured. The results showed that there were aggregates in the L-B films of metallophthalocyanines while not in the L-B films were examined by polarized UV-vis absorbance. It was confirmed that orientation in L-B films inherently depends upon those molecular states spreading monolayers on the water surface. According to this result, by introducing appropriate substitutents into porphyrin or phthalocyanine ring the molecular orientation and stracking in the L-B films could be controlled.
The monolayers on the water surface were studied by pressure-area isotherms, with five metalloporphyrins and metallophthalocyanines bearing differential substi-tuents. From the limiting areas together with the molecular model, probable orientation of maerocycle in the monolayer and the oriented effect of substituents upon the mac-rocycles were considered. These monolayer were transferred to the substrates by L-B method. The UV-vis spectra of the L-B films and in solution were measured. The results showed that there were aggregates in the L-B films of metallophthalocyanines while not in the L-B films were examined by polarized UV-vis absorbance. It was confirmed that orientation in L-B films inherently depends upon those molecular states spreading monolayers on the water surface. According to this result, by introducing appropriate substitutents into porphyrin or phthalocyanine ring the molecular orientation and stracking in the L-B films could be controlled.
1993, 9(04): 473-477
doi: 10.3866/PKU.WHXB19930410
Abstract:
For infinite lattice systems, we choose one atom as a reference point. Then one can remove a small cluster which contains the atom such that every atom in the cluster is part of at least one ring passing through the reference atom. A Bethe lattice is now introduced and connected to surface atom to simulate the effect of the rest of original system. Based on cluster-Bethe lattice model, we have calculated the energy of stabilization of SC, BCC and FCC and showed that BCC lattice is the stablest one at half-filled band so that it is indicated why simple substance crystals of column IA and VIB in periodic table are BCC structures.
For infinite lattice systems, we choose one atom as a reference point. Then one can remove a small cluster which contains the atom such that every atom in the cluster is part of at least one ring passing through the reference atom. A Bethe lattice is now introduced and connected to surface atom to simulate the effect of the rest of original system. Based on cluster-Bethe lattice model, we have calculated the energy of stabilization of SC, BCC and FCC and showed that BCC lattice is the stablest one at half-filled band so that it is indicated why simple substance crystals of column IA and VIB in periodic table are BCC structures.
1993, 9(04): 478-483
doi: 10.3866/PKU.WHXB19930411
Abstract:
The critical micelle activities (cma) of the mixed systems of sodium dodecylsul-fate-hexylpyridinehydrobromate have been determined by the drop-volume method under different ionic strengths (25 ℃). A formula to estimate the effect of inorganic salt electrolyte on the cma has been proposed.
The critical micelle activities (cma) of the mixed systems of sodium dodecylsul-fate-hexylpyridinehydrobromate have been determined by the drop-volume method under different ionic strengths (25 ℃). A formula to estimate the effect of inorganic salt electrolyte on the cma has been proposed.
1993, 9(04): 484-488
doi: 10.3866/PKU.WHXB19930412
Abstract:
A complete gas phase ultraviolet photoelectron spectrum(UPS) and HAM/3, MNDO, EHMO, MINDO/3, INDO as well as CNDO/2 molecular orbital calculations of pipera-zine-2,5-dione molecule are present in this paper. The tetra-multiple splitting peaks of the first band of piperazine-2,5-dione UPS spectrum have been assigned as the through-bond interactive aplittings which come from the oxygen and oxygen lone pairs, nitrogen and nitrogen lone pairs, respectively. And it has also shown that HAM/3 and MNDO calculations are better methods to predict the correct order of experimental ionization energies (I_(P_v)), orbital symmetry and the splitting spacing of through-bond and through-space interaction in-this molecule. MNDO optimum geometry of the molecule results in molecular plane conjugation and the reduction of throughbond splitting spacing.
A complete gas phase ultraviolet photoelectron spectrum(UPS) and HAM/3, MNDO, EHMO, MINDO/3, INDO as well as CNDO/2 molecular orbital calculations of pipera-zine-2,5-dione molecule are present in this paper. The tetra-multiple splitting peaks of the first band of piperazine-2,5-dione UPS spectrum have been assigned as the through-bond interactive aplittings which come from the oxygen and oxygen lone pairs, nitrogen and nitrogen lone pairs, respectively. And it has also shown that HAM/3 and MNDO calculations are better methods to predict the correct order of experimental ionization energies (I_(P_v)), orbital symmetry and the splitting spacing of through-bond and through-space interaction in-this molecule. MNDO optimum geometry of the molecule results in molecular plane conjugation and the reduction of throughbond splitting spacing.
1993, 9(04): 489-494
doi: 10.3866/PKU.WHXB19930413
Abstract:
A method for determining the sojourn time of adsorption of gas on solid surface by gas chromatography is presented. A theoretical equation has been derived. The method has been verified by the experimental adsorption data of eight alkanes and benzene on silica gel. And satisfactory results were t.
A method for determining the sojourn time of adsorption of gas on solid surface by gas chromatography is presented. A theoretical equation has been derived. The method has been verified by the experimental adsorption data of eight alkanes and benzene on silica gel. And satisfactory results were t.
1993, 9(04): 495-500
doi: 10.3866/PKU.WHXB19930414
Abstract:
Angle-resolved supersonic molecular beam scattering techniques are used to examine the angular distributions of the products formed in thermal and UV laser-induced reactions of chlorine molecular beam with InP(100) surface. For the thermal reaction, the angular distributions of InCl_2~+, InCl~+, PCl~+, PCl_2~+ and P_4~+ products are slightly peaked towards the normal of the surface and vary as cos~(1.5)θ, θ being the detection angle from the surface normal. The effect of the normal components of the transla-tional energies of Cl_2 molecules is also observed at different angle of incidence. Under 355 nm pulsed laser irradiation, the time-of-flight (TOF) spectra of InCl~+ are measured as a function of the detection angle and Maxwellian characterized with the mean kinetic energy or translational temperature. The flux distributions are sharper than cosine law and can be fitted by an expression of F(θ)=a·cosθ+(1-a)cos~nθ, where a and n are adjustable parameters. The mean kinetic energy distribution of InCl molecules is strongly peaked around the surface normal and decreases with increasing the detection angle. These results imply that both thermal and nonthermal desorption mechanisms are important in the UV laser-induced reaction processes.
Angle-resolved supersonic molecular beam scattering techniques are used to examine the angular distributions of the products formed in thermal and UV laser-induced reactions of chlorine molecular beam with InP(100) surface. For the thermal reaction, the angular distributions of InCl_2~+, InCl~+, PCl~+, PCl_2~+ and P_4~+ products are slightly peaked towards the normal of the surface and vary as cos~(1.5)θ, θ being the detection angle from the surface normal. The effect of the normal components of the transla-tional energies of Cl_2 molecules is also observed at different angle of incidence. Under 355 nm pulsed laser irradiation, the time-of-flight (TOF) spectra of InCl~+ are measured as a function of the detection angle and Maxwellian characterized with the mean kinetic energy or translational temperature. The flux distributions are sharper than cosine law and can be fitted by an expression of F(θ)=a·cosθ+(1-a)cos~nθ, where a and n are adjustable parameters. The mean kinetic energy distribution of InCl molecules is strongly peaked around the surface normal and decreases with increasing the detection angle. These results imply that both thermal and nonthermal desorption mechanisms are important in the UV laser-induced reaction processes.
1993, 9(04): 501-508
doi: 10.3866/PKU.WHXB19930415
Abstract:
V_2O_5 supported on various TiO_2 including anatase, rutile and mixture of both types have been investigated with various physicochemical measurements such as BET, TPD, NARP, XRD and so on. It has been found that the V=O species or the (010) plane of V_2O_5 on all the TiO_2 supports with large BET surface area are selectively exposed to the surface, though different modifications of TiO_2 results in different characteristics of exposure of (010) plane. For anatase, the maximum exposure of the V=O species is obtained at the surface concentration of V_2O_5 significantly lower than that for rutile. For the mixture, two maxima are obtained in the surface concentration of V_2O_5 corresponding to those for anatase and rutile respectively. Thus, it is concluded that crystal structure of the TiO_2 support determines the maximum exposure of (010) plane. The chemical activity of TiO_2 surface also seems to have an effect on the exposure of (010) plane. That is, the higher surface area and the stronger acidic property resulted in the high exposure of (010) plane.
V_2O_5 supported on various TiO_2 including anatase, rutile and mixture of both types have been investigated with various physicochemical measurements such as BET, TPD, NARP, XRD and so on. It has been found that the V=O species or the (010) plane of V_2O_5 on all the TiO_2 supports with large BET surface area are selectively exposed to the surface, though different modifications of TiO_2 results in different characteristics of exposure of (010) plane. For anatase, the maximum exposure of the V=O species is obtained at the surface concentration of V_2O_5 significantly lower than that for rutile. For the mixture, two maxima are obtained in the surface concentration of V_2O_5 corresponding to those for anatase and rutile respectively. Thus, it is concluded that crystal structure of the TiO_2 support determines the maximum exposure of (010) plane. The chemical activity of TiO_2 surface also seems to have an effect on the exposure of (010) plane. That is, the higher surface area and the stronger acidic property resulted in the high exposure of (010) plane.
1993, 9(04): 509-515
doi: 10.3866/PKU.WHXB19930416
Abstract:
A new concept, reduced extent of reaction, is introduced in this paper. Some new mathematical models of reversible reaction kinetics are suggested, and a reduced extent method for study of the thermokinetics of reversible reaction is proposed. A reversible reaction system, tris(hydroxymethyl) aminomethane with nitroethane in water(μ=1.0), has been studied with this method at 30.0 ℃. Rate constants and equilibrium constant calculated with this model are in fair agreement with that given in the literature. Thus, the correctness of the models and the validity of this method are proved.
A new concept, reduced extent of reaction, is introduced in this paper. Some new mathematical models of reversible reaction kinetics are suggested, and a reduced extent method for study of the thermokinetics of reversible reaction is proposed. A reversible reaction system, tris(hydroxymethyl) aminomethane with nitroethane in water(μ=1.0), has been studied with this method at 30.0 ℃. Rate constants and equilibrium constant calculated with this model are in fair agreement with that given in the literature. Thus, the correctness of the models and the validity of this method are proved.
1993, 9(04): 516-522
doi: 10.3866/PKU.WHXB19930417
Abstract:
The intrinsic protonation constants of three steps of chelating ion exchange resin D751 containing iminodiacetic groups in water and ethanol-water mixtures have been deter-mined at 25 ℃ by potentoimetric titration and by means of the extrapolation procedure without the assumption on the activity coefficients of charged species in the resin phase. The changes in the acid-base properties of the chelating resin D751 in the water and the ethanol-water mixtures have been obse-rved, and the observed effects are explained. The variation of apparent protonation constants with the degree of neutralizaton has been demonstrated.
The intrinsic protonation constants of three steps of chelating ion exchange resin D751 containing iminodiacetic groups in water and ethanol-water mixtures have been deter-mined at 25 ℃ by potentoimetric titration and by means of the extrapolation procedure without the assumption on the activity coefficients of charged species in the resin phase. The changes in the acid-base properties of the chelating resin D751 in the water and the ethanol-water mixtures have been obse-rved, and the observed effects are explained. The variation of apparent protonation constants with the degree of neutralizaton has been demonstrated.
1993, 9(04): 523-527
doi: 10.3866/PKU.WHXB19930418
Abstract:
POAP-Cu~+ is a od electrocatalyst for the reduction of O_2 into H_2O_2. It was found that Cu~(2+) can incorporate into POAP and form a stable POAP-Cu~+ film, which evidently electrocatalyzes the reduction of O_2 to produce H_2O_2. The rate constant of this reduction(k) is 4.33·10~2 (L·mol~(-1)·s~(-1)).
POAP-Cu~+ is a od electrocatalyst for the reduction of O_2 into H_2O_2. It was found that Cu~(2+) can incorporate into POAP and form a stable POAP-Cu~+ film, which evidently electrocatalyzes the reduction of O_2 to produce H_2O_2. The rate constant of this reduction(k) is 4.33·10~2 (L·mol~(-1)·s~(-1)).
1993, 9(04): 528-532
doi: 10.3866/PKU.WHXB19930419
Abstract:
Expressions for diffusion limiting currents at a microband electrode paired with a planar electrode of conventional size and with another microband electrode are derived analytically by conformal mapping. It is shown that the diffusion limiting currents depend on the microband electrode width L and the interelectrode gap width d, and they can be expressed as the ratio of the two complete elliptic functions K((square root(1-k~2)~(1/2))) and K(k), where k=(1+2L/d)~(-1) for band electrode pairs and k=(1+L/d)~(-1/2) for the band electrode near a planar electrode of conventional size.
Expressions for diffusion limiting currents at a microband electrode paired with a planar electrode of conventional size and with another microband electrode are derived analytically by conformal mapping. It is shown that the diffusion limiting currents depend on the microband electrode width L and the interelectrode gap width d, and they can be expressed as the ratio of the two complete elliptic functions K((square root(1-k~2)~(1/2))) and K(k), where k=(1+2L/d)~(-1) for band electrode pairs and k=(1+L/d)~(-1/2) for the band electrode near a planar electrode of conventional size.
1993, 9(04): 533-537
doi: 10.3866/PKU.WHXB19930420
Abstract:
2-mercaptobenzothiazole (2-HSBT) not only reacted with silver subcolloid and showed enhancing effect of the surface Raman scattering, but also reacted with the roughened silver electrode.
The normal Raman spectra (NRS) of benzothiazole compounds and their SERS adsorbed on the roughened silver electrode were investigated, the influences of the different substituting groups on NRS and SERS were also discussed.
2-mercaptobenzothiazole (2-HSBT) not only reacted with silver subcolloid and showed enhancing effect of the surface Raman scattering, but also reacted with the roughened silver electrode.
The normal Raman spectra (NRS) of benzothiazole compounds and their SERS adsorbed on the roughened silver electrode were investigated, the influences of the different substituting groups on NRS and SERS were also discussed.
1993, 9(04): 538-541
doi: 10.3866/PKU.WHXB19930421
Abstract:
The kinetic data related respectively to Co~(3+) anodic formation and O_2 anodic evolution at PbO_2 anode in 3.4 mol·kg~(-1) H_2SO_4+x mol·dm~(-3) COSO_4 (x=0.0501-0.350) and 0.2 mol·dm~(-3) CoSO_4+x mol·kg~(-1) H_2SO_4 (x=1.556-9.110) solutions were obtained by method of resolving the steady-state polarization curve. Steady-state φ～lgi relationships for Co~(3+) anodic formation reaction Tafel slope is close to 2.303RT/βF, whereas for O_2 anodic evolution it is close to 2.303RT/2βF (with β(?)0.5).
It is shown by experiment that the anodic formation of Co~(3+) and O_2 anodic evolution at PbO_2 anode in H_2SO_4 solutions are described by the equations:
i_1(O_2)=k_1a_W~4[Co~(2+)]exp2βφF/RT
i_2(Co~(3+))=k_2a_W[Co~(2+)]~(1.5)expβφF/RT
The experimental results may be explained by adopting the following scheme of electrode reactions
M+Co(H_2O)_6~(2-)+4H_2O→MCo(OH)_4(H_2O)_(2,ad)+4H_3O~++2e
2MCo(OH)_4(H_2O)_(2,ad)+2H_2O→O_2+2MCoO(H_2O)_(5,ad)
MCoO(H_2O)_(5,ad)+2H~+=M+Co(H_2O)_6~(2+)
MCo(OH)_4(H_2O)_(2,ad)+Co(H_2O)_6~(2+)→2Co(OH)_2(H_2O)_4~++M
Co(OH)_2(H_2O)_4~++2H~+=Co(H_2O)_6~(3+)
where M is an adsorption site on the PbO_2 anode.
The kinetic data related respectively to Co~(3+) anodic formation and O_2 anodic evolution at PbO_2 anode in 3.4 mol·kg~(-1) H_2SO_4+x mol·dm~(-3) COSO_4 (x=0.0501-0.350) and 0.2 mol·dm~(-3) CoSO_4+x mol·kg~(-1) H_2SO_4 (x=1.556-9.110) solutions were obtained by method of resolving the steady-state polarization curve. Steady-state φ～lgi relationships for Co~(3+) anodic formation reaction Tafel slope is close to 2.303RT/βF, whereas for O_2 anodic evolution it is close to 2.303RT/2βF (with β(?)0.5).
It is shown by experiment that the anodic formation of Co~(3+) and O_2 anodic evolution at PbO_2 anode in H_2SO_4 solutions are described by the equations:
i_1(O_2)=k_1a_W~4[Co~(2+)]exp2βφF/RT
i_2(Co~(3+))=k_2a_W[Co~(2+)]~(1.5)expβφF/RT
The experimental results may be explained by adopting the following scheme of electrode reactions
M+Co(H_2O)_6~(2-)+4H_2O→MCo(OH)_4(H_2O)_(2,ad)+4H_3O~++2e
2MCo(OH)_4(H_2O)_(2,ad)+2H_2O→O_2+2MCoO(H_2O)_(5,ad)
MCoO(H_2O)_(5,ad)+2H~+=M+Co(H_2O)_6~(2+)
MCo(OH)_4(H_2O)_(2,ad)+Co(H_2O)_6~(2+)→2Co(OH)_2(H_2O)_4~++M
Co(OH)_2(H_2O)_4~++2H~+=Co(H_2O)_6~(3+)
where M is an adsorption site on the PbO_2 anode.
1993, 9(04): 542-547
doi: 10.3866/PKU.WHXB19930422
Abstract:
A set of vapor-flow calorimeter has been constructed on the basis of Power's adiabatic calorimeter and Clarke s flash boiler. It can determine the heat capacities of mono-or multi-component vapors from vaporizing temperature to 600 K and 10—600 kPa pressures. For the calibration of the instrument, the heat capacities of benzene have been measured under 51.1, 101.3, 309.3 and 495.2 kPa and 370—600 K tempera-tures. For multicomponent vapor, benzene-cyclohexane has been determined. The results showed that the calorimeter has both the precision and accuracy better than 1.0% for either pure or mixtural vapors.
A set of vapor-flow calorimeter has been constructed on the basis of Power's adiabatic calorimeter and Clarke s flash boiler. It can determine the heat capacities of mono-or multi-component vapors from vaporizing temperature to 600 K and 10—600 kPa pressures. For the calibration of the instrument, the heat capacities of benzene have been measured under 51.1, 101.3, 309.3 and 495.2 kPa and 370—600 K tempera-tures. For multicomponent vapor, benzene-cyclohexane has been determined. The results showed that the calorimeter has both the precision and accuracy better than 1.0% for either pure or mixtural vapors.
1993, 9(04): 548-552
doi: 10.3866/PKU.WHXB19930423
Abstract:
The crystal structure of the title compound has been determined from single-crystal X-ray diffractometer data. (C_5H_7S_2)_2[Cu_3I_5] crystallizes in space group I 2/a with α=1.8126(12), b=0.9302(2), c=1.4275(2)nm, β=101.51(1)°and z= 4. The full-matrix least-squares refinement gave R=0.043 for 1820 observed [I>3.0σ(I)] reflections. The crystal structure consists of (C_5H_7S_2) cations and [Cu_3I_5]_∞ anions of infinite I-bridged chains, the repeat unit of which contains one three-coordinated copper(I) atom, the ligand configuration being approximatively tri nal planar, and two four-coordinated copper(I) atoms, possessing the ligand configuration of tetrahedron. The Cu—Cu distances are 0.2528(2) and 0.2557(2) nm, respectively.
The crystal structure of the title compound has been determined from single-crystal X-ray diffractometer data. (C_5H_7S_2)_2[Cu_3I_5] crystallizes in space group I 2/a with α=1.8126(12), b=0.9302(2), c=1.4275(2)nm, β=101.51(1)°and z= 4. The full-matrix least-squares refinement gave R=0.043 for 1820 observed [I>3.0σ(I)] reflections. The crystal structure consists of (C_5H_7S_2) cations and [Cu_3I_5]_∞ anions of infinite I-bridged chains, the repeat unit of which contains one three-coordinated copper(I) atom, the ligand configuration being approximatively tri nal planar, and two four-coordinated copper(I) atoms, possessing the ligand configuration of tetrahedron. The Cu—Cu distances are 0.2528(2) and 0.2557(2) nm, respectively.
1993, 9(04): 553-555
doi: 10.3866/PKU.WHXB19930424
Abstract:
We reported in this paper FTIR linear diehroic spectroscopy and anisotropic properties of the nanoparticulate α-Fe_2O_3-stearate alternating Langmuir-Blodgett films (Fe_2O_3-St LB films) a new inorganic-organic quantum superlattice system. A new method fitted to inorganic-organic alternating films is used to study the molecular orientation and discuss the order arrangement of the nanopartieles in the films. The the results show that a configuration of stearate ions bound to the surface of the nano-particles: COO~- group are spherically bound to the surface of the nanoparticles; the hydrocarbon chains are almost perpendicular (31°±5°) to the substrate (7 nm-Fe_2O_3-St LB films). The orientation of hydrocarbon chains and CH_2 scissors vibration show the existence of trans-zigzag planar structure for C—C broken bone of the hy7drocarbon chains, which is related to high-order structure of the alternate films.
We reported in this paper FTIR linear diehroic spectroscopy and anisotropic properties of the nanoparticulate α-Fe_2O_3-stearate alternating Langmuir-Blodgett films (Fe_2O_3-St LB films) a new inorganic-organic quantum superlattice system. A new method fitted to inorganic-organic alternating films is used to study the molecular orientation and discuss the order arrangement of the nanopartieles in the films. The the results show that a configuration of stearate ions bound to the surface of the nano-particles: COO~- group are spherically bound to the surface of the nanoparticles; the hydrocarbon chains are almost perpendicular (31°±5°) to the substrate (7 nm-Fe_2O_3-St LB films). The orientation of hydrocarbon chains and CH_2 scissors vibration show the existence of trans-zigzag planar structure for C—C broken bone of the hy7drocarbon chains, which is related to high-order structure of the alternate films.
1993, 9(04): 556-560
doi: 10.3866/PKU.WHXB19930425
Abstract:
A series of hindered triaryl-pyrazoline compounds have been synthesized. The photophysical behaviors of these compounds have also been studied. It was found that there were no evident change of the solvatochromism and the fluorescence quantum yield by the enhancement of the molecular conjugation and the inhibition of some specific bond rotation of these compounds. On the contrary, a remarkable effect on the photophysical behavior was observed when the intramolecular charge transfer ability was changed by the introduction of some substituted groups.
A series of hindered triaryl-pyrazoline compounds have been synthesized. The photophysical behaviors of these compounds have also been studied. It was found that there were no evident change of the solvatochromism and the fluorescence quantum yield by the enhancement of the molecular conjugation and the inhibition of some specific bond rotation of these compounds. On the contrary, a remarkable effect on the photophysical behavior was observed when the intramolecular charge transfer ability was changed by the introduction of some substituted groups.
1993, 9(04): 561-564
doi: 10.3866/PKU.WHXB19930426
Abstract:
Adsorption and reaction of CO on methanol synthesis catalyst have been studied with the pressure dynamic analysis equipment, The results show that the adsorbed CO on catalyst can be distinguished as reversibly adsorbed CO and irreverrsibly adsorbed CO. The irreversibly absorbed CO is necessary for the formation of CO_2, CH_4, etc. The formation of methanol is related with reversibly adsorbed CO. If there is not irrveer-sibly adsorbed H_2 on methanol synthesis catalyst, the catalyst has not methanol for-ming activity, and cannot adsorbs CO. So the part of irreversibly adsorbed H_2 which can be replaced by CO may be necessary for the adsorbed CO. The other part of irreversibly adsorbed H_2 which can not be replaced by CO may acted as a promoter of the catalyst.
Adsorption and reaction of CO on methanol synthesis catalyst have been studied with the pressure dynamic analysis equipment, The results show that the adsorbed CO on catalyst can be distinguished as reversibly adsorbed CO and irreverrsibly adsorbed CO. The irreversibly absorbed CO is necessary for the formation of CO_2, CH_4, etc. The formation of methanol is related with reversibly adsorbed CO. If there is not irrveer-sibly adsorbed H_2 on methanol synthesis catalyst, the catalyst has not methanol for-ming activity, and cannot adsorbs CO. So the part of irreversibly adsorbed H_2 which can be replaced by CO may be necessary for the adsorbed CO. The other part of irreversibly adsorbed H_2 which can not be replaced by CO may acted as a promoter of the catalyst.
1993, 9(04): 565-568
doi: 10.3866/PKU.WHXB19930427
Abstract:
The stability constants of binary complex eompounds formed by Ni(Ⅱ), Co(Ⅱ), Zn(Ⅱ)-N-(meta or para substituted phenyl) Iminodiacetic acid (m or p-RPhIDA) and of ternary complex compounds formed by Ni(Ⅱ), Co(Ⅱ), Zn(Ⅱ)-RPhIDA-Nitrilo-triacetic acid (NTA) were determined by pH method at 25±0.1 ℃ in the presence of 0.1 mol·dm~(-3)BaC_(10)_4. Their results were calculated by TITFIT program. It was found that linear free energy relationships did exist between the stability of there binary and ternary complex compounds and the base strengths of Ligands RPhIDA.
1993, 9(04): 569-574
doi: 10.3866/PKU.WHXB19930428
Abstract:
The dependence of the luminescence decay of electronically excited uranyl ions on the concentrations of uranium and sulphate in aqueous solution has been investigated with a pulsed nitrogen laser as a light source and a programmable transient recorder for lifetime measurements. Single exponential decay of the Luminescence is observed. The deactivation process of the excited uranyl ions should include radiative, nonradiative, water quenching and uranium self quenching and the measured lumine-scenec lifetime inidcates the result of all these processes. The Luminescence lifetime of uranyl ions increases with increasing concentration of sulphate and becomes constant when the equilibrium concentration of sulphate reaches 3.0 mol·L~(-1). The dependence of the Luminesence lifetime is similar to that of the UO_2(SO_4)_3~(4-) formation. This phenomenon can be interpreted in terms of the fact that in aqueous solution uranyl ions exist as aquo-uranyl ions. As the concentration of sulphte increaes the water molecule of hydrated uranyl ions will be replaced by sulphate ions via complex formation, and the quenching of excited uranyl ions by water is reduced. The self quenccing and the water quenching rate constants of UO_2(H_2O)_6~(2+) and UO_2(SO_4)_3~(4-) are estimated. Based on the experimental results a model for the deactivation mechanism of excited uranyl ions in sulphate solution is proposed.
The dependence of the luminescence decay of electronically excited uranyl ions on the concentrations of uranium and sulphate in aqueous solution has been investigated with a pulsed nitrogen laser as a light source and a programmable transient recorder for lifetime measurements. Single exponential decay of the Luminescence is observed. The deactivation process of the excited uranyl ions should include radiative, nonradiative, water quenching and uranium self quenching and the measured lumine-scenec lifetime inidcates the result of all these processes. The Luminescence lifetime of uranyl ions increases with increasing concentration of sulphate and becomes constant when the equilibrium concentration of sulphate reaches 3.0 mol·L~(-1). The dependence of the Luminesence lifetime is similar to that of the UO_2(SO_4)_3~(4-) formation. This phenomenon can be interpreted in terms of the fact that in aqueous solution uranyl ions exist as aquo-uranyl ions. As the concentration of sulphte increaes the water molecule of hydrated uranyl ions will be replaced by sulphate ions via complex formation, and the quenching of excited uranyl ions by water is reduced. The self quenccing and the water quenching rate constants of UO_2(H_2O)_6~(2+) and UO_2(SO_4)_3~(4-) are estimated. Based on the experimental results a model for the deactivation mechanism of excited uranyl ions in sulphate solution is proposed.
1993, 9(04): 575-576
doi: 10.3866/PKU.WHXB1993429
Abstract:
