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2004 Volume 20 Issue 8S
2004, 20(08S): 897-901
doi: 10.3866/PKU.WHXB200408zk01
Abstract:
Poly(methacrylic acid)/CdS (PMAA/CdS) spherical organic-inorganic composites with core-shell structures were prepared by utilizing polymeric microgel template effect on inorganic precipitation. The composites were produced via two steps. PMAA microgels containing Cd(Ac)2 were prepared by an inverse emulsion polymerization method. Then, H2S was introduced slowly into the system under stirring, and the metal ions were deposited within the microgels as CdS. The PMAA/CdS composites were obtained after washing treatment. The surface of the composites exhibited uniform micro- and nano-structured morphologies. Moreover, the surface structure of the micro-particles can be adjusted by changing the preparing conditions. In addition, ultrasound treatment makes the surface of particles much more smooth. XRD analysis shows that CdS in the composite is in crystalline state and is of face-centered structure. Furthermore, the composites are photoluminescence active due to presence of CdS.
Poly(methacrylic acid)/CdS (PMAA/CdS) spherical organic-inorganic composites with core-shell structures were prepared by utilizing polymeric microgel template effect on inorganic precipitation. The composites were produced via two steps. PMAA microgels containing Cd(Ac)2 were prepared by an inverse emulsion polymerization method. Then, H2S was introduced slowly into the system under stirring, and the metal ions were deposited within the microgels as CdS. The PMAA/CdS composites were obtained after washing treatment. The surface of the composites exhibited uniform micro- and nano-structured morphologies. Moreover, the surface structure of the micro-particles can be adjusted by changing the preparing conditions. In addition, ultrasound treatment makes the surface of particles much more smooth. XRD analysis shows that CdS in the composite is in crystalline state and is of face-centered structure. Furthermore, the composites are photoluminescence active due to presence of CdS.
2004, 20(08S): 902-905
doi: 10.3866/PKU.WHXB200408zk02
Abstract:
ZnO nanoparticles with different size were prepared by using sol-gel and precipitation method. With particle size of 10～50 nm, they were prepared by using precipitation method, and particle size and size distribution were controlled by milling process of an intermediate product Zn5(CO3)2(OH)6. With particle size smaller than 10 nm, they were synthesized by using sol-gel method, and the size was adjusted by changing the reaction conditions, such as reaction temperature, reaction time, etc. The ZnO nanoparticles with different size were characterized by using TEM, XRD, BET, UV-Vis. From UV-Vis spectra, the quantum effects of ZnO nanoparticles smaller than 10 nm were found, i.e., the absorption onset showed blueshifts with the decrease of size, and the ZnO nanoparticles bigger than 10 nm did not show quantum effects, the absorption edge was about 387 nm, corresponding to the bulk band gap for ZnO of 3.2 eV.
ZnO nanoparticles with different size were prepared by using sol-gel and precipitation method. With particle size of 10～50 nm, they were prepared by using precipitation method, and particle size and size distribution were controlled by milling process of an intermediate product Zn5(CO3)2(OH)6. With particle size smaller than 10 nm, they were synthesized by using sol-gel method, and the size was adjusted by changing the reaction conditions, such as reaction temperature, reaction time, etc. The ZnO nanoparticles with different size were characterized by using TEM, XRD, BET, UV-Vis. From UV-Vis spectra, the quantum effects of ZnO nanoparticles smaller than 10 nm were found, i.e., the absorption onset showed blueshifts with the decrease of size, and the ZnO nanoparticles bigger than 10 nm did not show quantum effects, the absorption edge was about 387 nm, corresponding to the bulk band gap for ZnO of 3.2 eV.
2004, 20(08S): 906-910
doi: 10.3866/PKU.WHXB200408zk03
Abstract:
A Ni/Ce-Zr-Al-Ox catalyst was prepared by hydrothermal synthesis－impregnation method. The CO2 reforming of CH4 reaction was performed. By XPS and TPH methods the carbon species deposited on the surface of catalyst during the reaction were characterized; The effect on the carbon deposit by adding a small amount of steam in feed gas and the interaction between steam and carbon species were studied. The results obtained show that there are mainly two types of carbon species :α-carbon appearing at 250～350 ℃ should be mainly CH4 decomposed fragment which shows reactive to hydrogenation; β-carbon appearing at about 700 ℃ should be the unreactive carbon which tends to be graphite or is graphitized carbon and is responsible for catalyst deactivation. β-carbon is easier to react with steam than α-carbon, therefore adding a small amount of steam in feed gas can obviously suppress β-carbon deposit. The activity test shows that the Ni/Ce-Zr-Al-Ox catalyst has a CH4 conversion of 89％ and a od stability, and the CH4 conversion increases to 94％ by adding 3.2％(φ) steam. In addition, due to the suppression to unreactive carbon, it can be expected that the stability of catalyst will be further promoted.
A Ni/Ce-Zr-Al-Ox catalyst was prepared by hydrothermal synthesis－impregnation method. The CO2 reforming of CH4 reaction was performed. By XPS and TPH methods the carbon species deposited on the surface of catalyst during the reaction were characterized; The effect on the carbon deposit by adding a small amount of steam in feed gas and the interaction between steam and carbon species were studied. The results obtained show that there are mainly two types of carbon species :α-carbon appearing at 250～350 ℃ should be mainly CH4 decomposed fragment which shows reactive to hydrogenation; β-carbon appearing at about 700 ℃ should be the unreactive carbon which tends to be graphite or is graphitized carbon and is responsible for catalyst deactivation. β-carbon is easier to react with steam than α-carbon, therefore adding a small amount of steam in feed gas can obviously suppress β-carbon deposit. The activity test shows that the Ni/Ce-Zr-Al-Ox catalyst has a CH4 conversion of 89％ and a od stability, and the CH4 conversion increases to 94％ by adding 3.2％(φ) steam. In addition, due to the suppression to unreactive carbon, it can be expected that the stability of catalyst will be further promoted.
2004, 20(08S): 911-916
doi: 10.3866/PKU.WHXB200408zk04
Abstract:
Eight possible unimolecular reaction pathways for ground-state pyruvic acid(PA) have been investigated in this work at the MP2/cc-pVDZ and B3LYP/cc-pVDZ levels of theory. The results indicate that hydrogen bond interaction and relative orientation of the two carbonyl groups play an important role in the stability of pyruvic acid rotamers. Moreover, the barriers for Tc isomerization to other isomers through internal rotation are high, suggesting that the isomerization reactions occur difficultly at room temperature. The barrier for transformation of Ct and Tt isomers through proton migration is higher than that through internal rotation, showing that the former cannot compete with the later. Under the investigation on decarboxylation and decarbonylation reactions, it can be concluded that the decarboxylation reaction takes place through stepwise mechanism involved in a five-center transition state and produces methyl hydroxycarbene firstly, and the concerted mechanism associated with a four-center transition state is disadvantageous.
Eight possible unimolecular reaction pathways for ground-state pyruvic acid(PA) have been investigated in this work at the MP2/cc-pVDZ and B3LYP/cc-pVDZ levels of theory. The results indicate that hydrogen bond interaction and relative orientation of the two carbonyl groups play an important role in the stability of pyruvic acid rotamers. Moreover, the barriers for Tc isomerization to other isomers through internal rotation are high, suggesting that the isomerization reactions occur difficultly at room temperature. The barrier for transformation of Ct and Tt isomers through proton migration is higher than that through internal rotation, showing that the former cannot compete with the later. Under the investigation on decarboxylation and decarbonylation reactions, it can be concluded that the decarboxylation reaction takes place through stepwise mechanism involved in a five-center transition state and produces methyl hydroxycarbene firstly, and the concerted mechanism associated with a four-center transition state is disadvantageous.
2004, 20(08S): 917-923
doi: 10.3866/PKU.WHXB200408zk05
Abstract:
The development of the coordination chemistry of diazamesocycles, mainly on the most typical 1,5-dizacyclooctane (DACO) and its functionalized derivatives, are briefly reviewed. Our investigations on this aspect were highlighted.
The development of the coordination chemistry of diazamesocycles, mainly on the most typical 1,5-dizacyclooctane (DACO) and its functionalized derivatives, are briefly reviewed. Our investigations on this aspect were highlighted.
2004, 20(08S): 924-929
doi: 10.3866/PKU.WHXB200408zk06
Abstract:
The effects of the rigidity of molecular recognition sites in fluorine-based conjugated polymers P1 and P2 in solution on metal ion sensing have been investigated. The structures of polymer P1 and P2 have twisted 2,2′-bipyridine and planar 1,10-phenanthroline units, respectively, which alternate with one fluorene monomer unit. It is found that absorption and emission bands of 1,10-phenanthroline-based polymer P2 exposed to metal ions can be red -shifted up to 30 nm, and emission intensity can be quenched up to 100％, depending on metal ions present, which is very similar to the behavoir of 2,2′-bipyridine-based analog P1. And P2 shows much higher sensitivity to metal ion than that of P1. The origins of ionochromic effects of 2,2′-bipyridine-based conjugated polymer due to the metal ion chelation have been attributed to both conformational changes and electron density variations on the polymer chains caused by introducing positively charged metal ions. Based on the fact that conformational changes are not required in the ion responsive process of phen ion-recognition unit, we demonstrate that the electron density variations play more important roles in metal ion induced red shifts in absorption and fluorescence quenching in photoluminescence. The higher sensitivity of P2 films to metal ions compared with P1 suggest the use of rigid units as molecular recognition sites in the fluorescent ions-sensory conjugated polymer for achieving higher sensing sensitivity, which is also significant for studying the nature of ionchromatic effect of conjugated polymer. The study present herein has, to a certain degree, elucidated the nature of metal ion and polymer interactions and demonstrated a new approach to improve the metal ions sensing properties of conjugated polymer.
The effects of the rigidity of molecular recognition sites in fluorine-based conjugated polymers P1 and P2 in solution on metal ion sensing have been investigated. The structures of polymer P1 and P2 have twisted 2,2′-bipyridine and planar 1,10-phenanthroline units, respectively, which alternate with one fluorene monomer unit. It is found that absorption and emission bands of 1,10-phenanthroline-based polymer P2 exposed to metal ions can be red -shifted up to 30 nm, and emission intensity can be quenched up to 100％, depending on metal ions present, which is very similar to the behavoir of 2,2′-bipyridine-based analog P1. And P2 shows much higher sensitivity to metal ion than that of P1. The origins of ionochromic effects of 2,2′-bipyridine-based conjugated polymer due to the metal ion chelation have been attributed to both conformational changes and electron density variations on the polymer chains caused by introducing positively charged metal ions. Based on the fact that conformational changes are not required in the ion responsive process of phen ion-recognition unit, we demonstrate that the electron density variations play more important roles in metal ion induced red shifts in absorption and fluorescence quenching in photoluminescence. The higher sensitivity of P2 films to metal ions compared with P1 suggest the use of rigid units as molecular recognition sites in the fluorescent ions-sensory conjugated polymer for achieving higher sensing sensitivity, which is also significant for studying the nature of ionchromatic effect of conjugated polymer. The study present herein has, to a certain degree, elucidated the nature of metal ion and polymer interactions and demonstrated a new approach to improve the metal ions sensing properties of conjugated polymer.
2004, 20(08S): 930-935
doi: 10.3866/PKU.WHXB200408zk07
Abstract:
The intramolecular charge transfer (CT) reaction known to occur in benzanilide（BA） derivatives was coupled to salicylic acid (SA) for understanding the substituent effect on the proton transfer fluorescence in comparison with that on the CT fluorescence. A series of salicylanilides 1, in which the SA structural framework was incorporated in the electron acceptor moiety of the BA-like CT fluorophore, were designed and their absorption and fluorescence spectra were investigated in aprotic solvents CHX, DEE, and ACN and a protic solvent MeOH. It was found that 1 exhibited a long-wavelength emission at 470 nm in CHX that scarcely shifted when solvent changed from DEE to ACN of increasing polarity, whereas it drastically shifted to blue at ca 430 nm in protic solvent MeOH. It was therefore made clear that the emission of 1 was different from that of benzanilide, the latter being highly sensitive to solvent polarity. With 2,the o-OH methylated derivatives of 1, long-wavelength fluorescence emission with similar solvent dependence to that of benzanilides was observed. These facts suggested that the emission from 1 originated from the SA-like PT state while that of 2 from the BA-like CT state. The substituent effect on the emission of 1 and 2 with p- or m-substituent at the anilino phenyl ring was examined. Results showed that, whereas the emission of 1 scarcely varied, that of 2 dramatically shifted to the blue with increasing electron-withdrawing ability of the substituent. The emission energies of 2 in CHX were found to be correlated linearly to the Hammett constants of the substituents with a slope of ＋0.378 eV, close to ＋0.361 eV observed for benzanilides. It was concluded that the emission of 1 originated from the PT state that showed practically no dependence on solvent polarity and substituent at the proton acceptor moiety.
The intramolecular charge transfer (CT) reaction known to occur in benzanilide（BA） derivatives was coupled to salicylic acid (SA) for understanding the substituent effect on the proton transfer fluorescence in comparison with that on the CT fluorescence. A series of salicylanilides 1, in which the SA structural framework was incorporated in the electron acceptor moiety of the BA-like CT fluorophore, were designed and their absorption and fluorescence spectra were investigated in aprotic solvents CHX, DEE, and ACN and a protic solvent MeOH. It was found that 1 exhibited a long-wavelength emission at 470 nm in CHX that scarcely shifted when solvent changed from DEE to ACN of increasing polarity, whereas it drastically shifted to blue at ca 430 nm in protic solvent MeOH. It was therefore made clear that the emission of 1 was different from that of benzanilide, the latter being highly sensitive to solvent polarity. With 2,the o-OH methylated derivatives of 1, long-wavelength fluorescence emission with similar solvent dependence to that of benzanilides was observed. These facts suggested that the emission from 1 originated from the SA-like PT state while that of 2 from the BA-like CT state. The substituent effect on the emission of 1 and 2 with p- or m-substituent at the anilino phenyl ring was examined. Results showed that, whereas the emission of 1 scarcely varied, that of 2 dramatically shifted to the blue with increasing electron-withdrawing ability of the substituent. The emission energies of 2 in CHX were found to be correlated linearly to the Hammett constants of the substituents with a slope of ＋0.378 eV, close to ＋0.361 eV observed for benzanilides. It was concluded that the emission of 1 originated from the PT state that showed practically no dependence on solvent polarity and substituent at the proton acceptor moiety.
2004, 20(08S): 936-938
doi: 10.3866/PKU.WHXB200408zk08
Abstract:
Certain reactions are catalyzed on the polar stratospheric clouds to produce HOCl and Cl2 which can be turned into Cl by the UV light from the sun, and Cl is believed to be the arch-criminal in the atmospheric ozone depletion. The traditional ion-catalysis mechanism was based on the suggestion by Molina, a Nobel Prize laureate. However, more and more facts have indicated that this mechanism needs to be revised. Zhao Xin-Sheng's group first proposed a mechanism of structure catalysis, which relies on the surface structure of the ice. The mechanism has been confirmed by new experimental and theoretical studies. This paper briefly reviews some key development in recent years.
Certain reactions are catalyzed on the polar stratospheric clouds to produce HOCl and Cl2 which can be turned into Cl by the UV light from the sun, and Cl is believed to be the arch-criminal in the atmospheric ozone depletion. The traditional ion-catalysis mechanism was based on the suggestion by Molina, a Nobel Prize laureate. However, more and more facts have indicated that this mechanism needs to be revised. Zhao Xin-Sheng's group first proposed a mechanism of structure catalysis, which relies on the surface structure of the ice. The mechanism has been confirmed by new experimental and theoretical studies. This paper briefly reviews some key development in recent years.
2004, 20(08S): 939-945
doi: 10.3866/PKU.WHXB200408zk09
Abstract:
Conventionally, heterogeneous catalysts are mainly focused on the materials with large surface area such as TS-1 (350 m2•g－1),and the materials with relatively small surface area ( < 10 m2•g－1) are generally ignored. This review summarized the catalytic activities and mechanism in a series of oxidations by H2O2 or oxygen as oxidants over novel copper phosphates with very small surface area less than 1.4 m2•g－1.In the hydroxylation of phenol and benzene by H2O2, the high activities of this catalyst are comparable to those of TS-1. In epoxidation of styrene by H2O2, the selectivity for epoxide is much higher than that of TS-1. In hydroxylation of 2,3,6-trimethylphenol by H2O2, it showed od activity and high selectivity for trimethylhydroquinone. In oxidation of olefins and alcohols by O2, the catalysts exhibited remarkable catalytic results. The characterization of ESR and IR spectroscopy shows that hydroxyl radicals and peroxide species are important intermediates in these oxidations.
Conventionally, heterogeneous catalysts are mainly focused on the materials with large surface area such as TS-1 (350 m2•g－1),and the materials with relatively small surface area ( < 10 m2•g－1) are generally ignored. This review summarized the catalytic activities and mechanism in a series of oxidations by H2O2 or oxygen as oxidants over novel copper phosphates with very small surface area less than 1.4 m2•g－1.In the hydroxylation of phenol and benzene by H2O2, the high activities of this catalyst are comparable to those of TS-1. In epoxidation of styrene by H2O2, the selectivity for epoxide is much higher than that of TS-1. In hydroxylation of 2,3,6-trimethylphenol by H2O2, it showed od activity and high selectivity for trimethylhydroquinone. In oxidation of olefins and alcohols by O2, the catalysts exhibited remarkable catalytic results. The characterization of ESR and IR spectroscopy shows that hydroxyl radicals and peroxide species are important intermediates in these oxidations.
2004, 20(08S): 946-952
doi: 10.3866/PKU.WHXB200408zk10
Abstract:
In this article some latest research progresses in adsorption and catalytic degradation of nitrosamines by use of zeolites and mesoporous molecular sieves are reviewed, along with the oversea and domestic development of microanalysis of nitrosamines. Nitrosamines in tobacco smoke are strong carcinogenic compounds inducing cancer for smoking, so zeolite is recently employed, as additive to eliminate nitrosamines in smoke, to protect environment and public health. The selective adsorption of nitrosamines on zeolite, especially the inserting adsorption model of bulky nitrosamines on the zeolites with small pore size is introduced in this review. For the selective adsorption by zeolite of the volatile nitrosamines in gaseous phase or solution, some factors and their influences on the adsorption are briefly discussed. The high activity of mesoporous molecular sieves in catalytic degradation of tobacco specific nitrosamines is also presented and attributed to their large pore sizes. Moreover, the modifications of zeolite with metal oxides such as copper oxide are introduced, which significantly promote the selectively adsorption of volatile nitrosamines, and are beneficial for removal of the nitrosamines in smoke of cigarette. Finally, the development of new functional materials to eliminate the pollution of nitrosamines is prospected.
In this article some latest research progresses in adsorption and catalytic degradation of nitrosamines by use of zeolites and mesoporous molecular sieves are reviewed, along with the oversea and domestic development of microanalysis of nitrosamines. Nitrosamines in tobacco smoke are strong carcinogenic compounds inducing cancer for smoking, so zeolite is recently employed, as additive to eliminate nitrosamines in smoke, to protect environment and public health. The selective adsorption of nitrosamines on zeolite, especially the inserting adsorption model of bulky nitrosamines on the zeolites with small pore size is introduced in this review. For the selective adsorption by zeolite of the volatile nitrosamines in gaseous phase or solution, some factors and their influences on the adsorption are briefly discussed. The high activity of mesoporous molecular sieves in catalytic degradation of tobacco specific nitrosamines is also presented and attributed to their large pore sizes. Moreover, the modifications of zeolite with metal oxides such as copper oxide are introduced, which significantly promote the selectively adsorption of volatile nitrosamines, and are beneficial for removal of the nitrosamines in smoke of cigarette. Finally, the development of new functional materials to eliminate the pollution of nitrosamines is prospected.
2004, 20(08S): 953-965
doi: 10.3866/PKU.WHXB200408zk11
Abstract:
This article describes the capabilities of coupled UHV-electrochemistry as a means to obtain the microscopic information of the electrode-solution interface. It presents the experimental aspects for sample preparation and surface analytical techniques and some selected studies of the recent results with single-crystal electrode surfaces; the phase transition for the reconstructed Au(100)-hex and Pt(100)-hex electrodes in the electrochemical cell and the structural study of the epitaxial growth of Pt on Ru(0001) and Ru(1010) surfaces as well as the growth of RuO2(100) on Ru(0001).
This article describes the capabilities of coupled UHV-electrochemistry as a means to obtain the microscopic information of the electrode-solution interface. It presents the experimental aspects for sample preparation and surface analytical techniques and some selected studies of the recent results with single-crystal electrode surfaces; the phase transition for the reconstructed Au(100)-hex and Pt(100)-hex electrodes in the electrochemical cell and the structural study of the epitaxial growth of Pt on Ru(0001) and Ru(1010) surfaces as well as the growth of RuO2(100) on Ru(0001).
2004, 20(08S): 966-973
doi: 10.3866/PKU.WHXB200408zk12
Abstract:
The relativistic density functional computational methods applicable to the calculation of systems containing heavy elements with high accuracy are simply reviewed. In connection with the researches carried out in our laboratory, the description is concentrated on the high accurate four-component relativistic density functional methods with relativistic effects taken into account strictly, and the two-component or scalar relativistic density functional methods with relativistic effects considered approximately, involving the zero-order regular approximation (ZORA) method and its improved variants, the singularity excluded approximate expansion (SEAX) method, and the jointed two component-scalar relativistic (or non-relativistic) approach applicable to the calculations of large systems locally containing heavy elements.
The relativistic density functional computational methods applicable to the calculation of systems containing heavy elements with high accuracy are simply reviewed. In connection with the researches carried out in our laboratory, the description is concentrated on the high accurate four-component relativistic density functional methods with relativistic effects taken into account strictly, and the two-component or scalar relativistic density functional methods with relativistic effects considered approximately, involving the zero-order regular approximation (ZORA) method and its improved variants, the singularity excluded approximate expansion (SEAX) method, and the jointed two component-scalar relativistic (or non-relativistic) approach applicable to the calculations of large systems locally containing heavy elements.
2004, 20(08S): 974-981
doi: 10.3866/PKU.WHXB200408zk13
Abstract:
In chemiluminescence measurements, an interesting development of analytical significance is the incorporation of micelle into the detection system, which has achievements of multiple benefits such as enhanced sensitivity, improved selectivity and experimental convenience. In this review, normal and reversed micelle enhancement on chemiluminescence(CL) energy transfer is described. The different chemiluminescence systems in conjunction with energy transfer and the interactions with the micelle enhancement are presented. In micelle media, a combination of changes in excitation efficiency, fluorescence efficiency, and the reaction rate of the CL system results in an increase of the CL intensity.
In chemiluminescence measurements, an interesting development of analytical significance is the incorporation of micelle into the detection system, which has achievements of multiple benefits such as enhanced sensitivity, improved selectivity and experimental convenience. In this review, normal and reversed micelle enhancement on chemiluminescence(CL) energy transfer is described. The different chemiluminescence systems in conjunction with energy transfer and the interactions with the micelle enhancement are presented. In micelle media, a combination of changes in excitation efficiency, fluorescence efficiency, and the reaction rate of the CL system results in an increase of the CL intensity.
2004, 20(08S): 982-988
doi: 10.3866/PKU.WHXB200408zk14
Abstract:
In this review, we evaluate the present state in the field of monolayer protected metal nanoclusters with regard to their synthesis, their optical and electrochemical properties and applications. Their quantum capacitance charging phenomenon and electroactive monolayer protected nanoclusters were especially stressed. Finally, we canvass some of the important remaining research opportunities in this field and present a brief outlook. We believe that progresses in this field would greatly promote the development of chemistry, biochemistry and material chemistry.
In this review, we evaluate the present state in the field of monolayer protected metal nanoclusters with regard to their synthesis, their optical and electrochemical properties and applications. Their quantum capacitance charging phenomenon and electroactive monolayer protected nanoclusters were especially stressed. Finally, we canvass some of the important remaining research opportunities in this field and present a brief outlook. We believe that progresses in this field would greatly promote the development of chemistry, biochemistry and material chemistry.
2004, 20(08S): 989-994
doi: 10.3866/PKU.WHXB200408zk15
Abstract:
This paper reviews the transition metal complexes such as Ni, Pd, Pt, Rh, Cu-catalyzed activation of hetero－carbon bonds and the related catalytic addition reactions with alkynes. These new addition reactions provide one-step, atom-economic methods for the preparation of the functionalized alkenes, which have R3Si, R3Sn, RS, RSe, Cl and Br groups. The addition reactions proceed with high stereoselectivities and regioselectivities.
This paper reviews the transition metal complexes such as Ni, Pd, Pt, Rh, Cu-catalyzed activation of hetero－carbon bonds and the related catalytic addition reactions with alkynes. These new addition reactions provide one-step, atom-economic methods for the preparation of the functionalized alkenes, which have R3Si, R3Sn, RS, RSe, Cl and Br groups. The addition reactions proceed with high stereoselectivities and regioselectivities.
2004, 20(08S): 995-1002
doi: 10.3866/PKU.WHXB200408zk16
Abstract:
In this review the highlights of both experimental and theoretical studies on single molecular device as well as the standard elastic electronic transport theory combining with Green′s function technique are introduced concisely. A theoretical study on transport properties of a H2O molecule bridged between two Au(111) surface is carried out by using full self-consistent first-principles method and non-equilibrium Green′s functions method. The results show that there is a strong hybridization between H2O molecule and Au surface atoms of the electrodes. The molecular character of H2O molecule is largely conserved by states of Au atoms of electrodes at a small bias voltage. The potential distribution locates the local region around H2O molecule. The conductance of a single H2O molecule bridged between two Au electrodes is mainly contributed by a single channel.
In this review the highlights of both experimental and theoretical studies on single molecular device as well as the standard elastic electronic transport theory combining with Green′s function technique are introduced concisely. A theoretical study on transport properties of a H2O molecule bridged between two Au(111) surface is carried out by using full self-consistent first-principles method and non-equilibrium Green′s functions method. The results show that there is a strong hybridization between H2O molecule and Au surface atoms of the electrodes. The molecular character of H2O molecule is largely conserved by states of Au atoms of electrodes at a small bias voltage. The potential distribution locates the local region around H2O molecule. The conductance of a single H2O molecule bridged between two Au electrodes is mainly contributed by a single channel.
2004, 20(08S): 1003-1009
doi: 10.3866/PKU.WHXB200408zk17
Abstract:
We provide a brief survey of recent results on the electronic transport characteristics of single molecules as well as self-assembled monolayers (SAM).
We provide a brief survey of recent results on the electronic transport characteristics of single molecules as well as self-assembled monolayers (SAM).
2004, 20(08S): 1010-1016
doi: 10.3866/PKU.WHXB200408zk18
Abstract:
The principle of wave-particle duality of quantum mechanics ascertains that any microscopic particle must also exhibit wave properties. The matter wave, or de Broglie wave, was first evidenced by Davisson and Germer in 1927 in the electron diffraction by crystals. In recent years, numerous fascinating examples of the quantum interference effect (QIE) have been discovered in the molecular systems in their excitation, dissociation and ionization by photons as well as in collision processes. Our group was the first to obtain the experimental evidence of QIE in a collision, specifically for the singlet-triplet mixed state of a diatomic species, and to derive an explicit expression for its energy transfer cross-section. In this expression, the interference phase angle (θST) that describes the phase angle difference between singlet and triplet energy transfer channels is defined and experimentally measured for CO(A 1Π,v=0/e 3Σ－,v =1)-M collision system with M= rare gases (He, Ne, Ar), homonuclear diatomics (H2, N2, O2) and heteronuclear diatomics (HCl) via the optical-optical double resonance multiphoton ionization (OODR-MPI) technique. We have also observed QIE in Na2(A 1Σu＋, v=8/b 3Π0u, v =14)-Na collision. More recently, we have carried out quantum scattering calculations of the interference angle based on the first order Born approximation of time dependent perturbation theory. For atom-diatom collision,the anisotropic Lennard-Jones interaction potential was adopted, and for polar diatom-diatom collision, the long-range dipole-dipole interaction proportional to R－3 was shown to be a proper potential for the calculation. All the calculated θST at T=77,253 and 470 K for CO(A 1Π,v=0/e 3Σ－, v =1)-M, for M=He(θST=58°～65°), Ne(66°～69°), Ar(72°～90°) and HCl(101°～110°), are in od agreement with the experiments. Our calculated differential θST are in the range of 48°～70° for CO-He and 93°～112° for CO-HCl collision for all v and b values that are physically significant. These values are close to those experimental θST′s obtained in the gas cell, implying that the “average effect” is not serious. The calculation also gives an effective collision time of 0.3 ps for CO－He and 1.5 ps for CO－HCl collision, which explains why the experimental θST for the former is much smaller than that of the latter. These results show that θST should provide important information on the singlet-triplet mixed state intermolecular potential, which is difficult to obtain by other experimental or theoretical methods.
The principle of wave-particle duality of quantum mechanics ascertains that any microscopic particle must also exhibit wave properties. The matter wave, or de Broglie wave, was first evidenced by Davisson and Germer in 1927 in the electron diffraction by crystals. In recent years, numerous fascinating examples of the quantum interference effect (QIE) have been discovered in the molecular systems in their excitation, dissociation and ionization by photons as well as in collision processes. Our group was the first to obtain the experimental evidence of QIE in a collision, specifically for the singlet-triplet mixed state of a diatomic species, and to derive an explicit expression for its energy transfer cross-section. In this expression, the interference phase angle (θST) that describes the phase angle difference between singlet and triplet energy transfer channels is defined and experimentally measured for CO(A 1Π,v=0/e 3Σ－,v =1)-M collision system with M= rare gases (He, Ne, Ar), homonuclear diatomics (H2, N2, O2) and heteronuclear diatomics (HCl) via the optical-optical double resonance multiphoton ionization (OODR-MPI) technique. We have also observed QIE in Na2(A 1Σu＋, v=8/b 3Π0u, v =14)-Na collision. More recently, we have carried out quantum scattering calculations of the interference angle based on the first order Born approximation of time dependent perturbation theory. For atom-diatom collision,the anisotropic Lennard-Jones interaction potential was adopted, and for polar diatom-diatom collision, the long-range dipole-dipole interaction proportional to R－3 was shown to be a proper potential for the calculation. All the calculated θST at T=77,253 and 470 K for CO(A 1Π,v=0/e 3Σ－, v =1)-M, for M=He(θST=58°～65°), Ne(66°～69°), Ar(72°～90°) and HCl(101°～110°), are in od agreement with the experiments. Our calculated differential θST are in the range of 48°～70° for CO-He and 93°～112° for CO-HCl collision for all v and b values that are physically significant. These values are close to those experimental θST′s obtained in the gas cell, implying that the “average effect” is not serious. The calculation also gives an effective collision time of 0.3 ps for CO－He and 1.5 ps for CO－HCl collision, which explains why the experimental θST for the former is much smaller than that of the latter. These results show that θST should provide important information on the singlet-triplet mixed state intermolecular potential, which is difficult to obtain by other experimental or theoretical methods.
2004, 20(08S): 1017-1023
doi: 10.3866/PKU.WHXB200408zk19
Abstract:
Surface systems composed of low-dimensional nanomaterials have been attracted extensive attentions and applied in many fields such as electrocatalysis, magnetism, energy storage and sensing. The enhanced IR absorption and abnormal IR effects are their anomalous IR optical properties. This paper reviews our recent progress in studying the enhanced IR absorption and abnormal IR effects of low-dimensional nanomaterials. The study consists of the systematic preparation of nanometer scale-thin films and nanoparticles and building surface nanostructures that exhibit anomalous IR properties, as well as in the development of surface combinatorial method, etc. The study is of importance in revealing the intrinsic relationship between anomalous IR optical property and nanostructure of low-dimensional nanomaterials, and in developing related fundamentals.
Surface systems composed of low-dimensional nanomaterials have been attracted extensive attentions and applied in many fields such as electrocatalysis, magnetism, energy storage and sensing. The enhanced IR absorption and abnormal IR effects are their anomalous IR optical properties. This paper reviews our recent progress in studying the enhanced IR absorption and abnormal IR effects of low-dimensional nanomaterials. The study consists of the systematic preparation of nanometer scale-thin films and nanoparticles and building surface nanostructures that exhibit anomalous IR properties, as well as in the development of surface combinatorial method, etc. The study is of importance in revealing the intrinsic relationship between anomalous IR optical property and nanostructure of low-dimensional nanomaterials, and in developing related fundamentals.
2004, 20(08S): 1024-1031
doi: 10.3866/PKU.WHXB200408zk20
Abstract:
In situ MAS NMR spectroscopy has been successfully applied to study catalytic reaction mechanisms. Examples taken from our own study illustrate that the batch-like condition in situ MAS NMR technique with strategically 13C labeled reactants can contribute to the understanding of reaction pathway. The results indicate that the ion-exchanged and/or its related Ga species are the highly active catalytic components for the activation of propane under mild condition over Ga-modified H-MFI catalysts. Reaction mechanism of skeletal isomerization of n-butane over a series of solid acid catalysts in the acidic strength order of SO42-/ZrO2, CsxH3－xPW12O40 and H-MOR was also studied. The mechanism of n-butane isomerization is dependent on the type of solid acid catalyst. Under low temperature, n-butane isomerization on SO42-/ZrO2 and CsxH3－xPW12O40 catalysts proceeds through a monomolecular pathway in the initial stage of the reaction. At the later stage, C3 and C5 are detected, giving the evidence of the contribution of the bimolecular process. On H-MOR catalyst, n-butane isomerization occurs primarily via a bimolecular pathway. Further study shows that the kinetics of n-butane isomerization on SO42-/ZrO2 catalyst at ambient temperature can be well represented by Langmuir-Hinshelwood equation for a reversible first order surface reaction. The calculated isomerization reaction rate constant can be used as a measure of the solid superacidity of the catalysts.
In situ MAS NMR spectroscopy has been successfully applied to study catalytic reaction mechanisms. Examples taken from our own study illustrate that the batch-like condition in situ MAS NMR technique with strategically 13C labeled reactants can contribute to the understanding of reaction pathway. The results indicate that the ion-exchanged and/or its related Ga species are the highly active catalytic components for the activation of propane under mild condition over Ga-modified H-MFI catalysts. Reaction mechanism of skeletal isomerization of n-butane over a series of solid acid catalysts in the acidic strength order of SO42-/ZrO2, CsxH3－xPW12O40 and H-MOR was also studied. The mechanism of n-butane isomerization is dependent on the type of solid acid catalyst. Under low temperature, n-butane isomerization on SO42-/ZrO2 and CsxH3－xPW12O40 catalysts proceeds through a monomolecular pathway in the initial stage of the reaction. At the later stage, C3 and C5 are detected, giving the evidence of the contribution of the bimolecular process. On H-MOR catalyst, n-butane isomerization occurs primarily via a bimolecular pathway. Further study shows that the kinetics of n-butane isomerization on SO42-/ZrO2 catalyst at ambient temperature can be well represented by Langmuir-Hinshelwood equation for a reversible first order surface reaction. The calculated isomerization reaction rate constant can be used as a measure of the solid superacidity of the catalysts.
2004, 20(08S): 1032-1036
doi: 10.3866/PKU.WHXB200408zk21
Abstract:
A general treatment of nonadiabatic quantum dynamics with split-operator scheme on multiple interacting potential surfaces has been presented. The applications of this method in reaction scattering, photodissociation, and energy transfer have been reviewed.
A general treatment of nonadiabatic quantum dynamics with split-operator scheme on multiple interacting potential surfaces has been presented. The applications of this method in reaction scattering, photodissociation, and energy transfer have been reviewed.
2004, 20(08S): 1037-1044
doi: 10.3866/PKU.WHXB200408zk22
Abstract:
This paper reviews our work on dynamical localization of the two-level system (TLS). By mapping the quantum dynamics of a driven TLS to the classical one of a particle experiencing a two-dimensional harmonic force as well as a periodic magnetic field, deep insights into the mechanism of localization have been gained. Using this scheme we are able to obtain the condition for localization of a TLS subject to the linearly polarized field. The localization induced by δ-function pulses and circularly polarized fields has been analytically investigated. It is found that the circularly-polarized-field induced localization can be fully described by the geometry of an ellipse within a unit circle on a complex plane.
This paper reviews our work on dynamical localization of the two-level system (TLS). By mapping the quantum dynamics of a driven TLS to the classical one of a particle experiencing a two-dimensional harmonic force as well as a periodic magnetic field, deep insights into the mechanism of localization have been gained. Using this scheme we are able to obtain the condition for localization of a TLS subject to the linearly polarized field. The localization induced by δ-function pulses and circularly polarized fields has been analytically investigated. It is found that the circularly-polarized-field induced localization can be fully described by the geometry of an ellipse within a unit circle on a complex plane.
2004, 20(08S): 1045-1054
doi: 10.3866/PKU.WHXB200408zk23
Abstract:
The research on the cluster modeling of chemisorption and reactions on metal oxide surfaces in our group has been reviewed. Three principles, namely, neutrality principle, stoichiometrical principle and coordination principle were proposed for building up cluster models of metal oxides. od correlation between the topologic parameters Nc(βc), Na(βa) and Nd(βd) with the stability of clusters has been shown. The problem of how the ways of embedding affect the calculated electronic properties of the substrate clusters and the adsorption properties has been investigated. Based on these, we proposed an SPC model, which is a stoichiometric cutout cluster embedded in a spherically expanded point charge surrounding with charges being self-consistently determined. We have successfully applied the SPC model to a variety of important systems, including H2/ZnO, O/M , NO/M , N2O/M , N2O/Li/M , CO/M and CO/NiO.
The research on the cluster modeling of chemisorption and reactions on metal oxide surfaces in our group has been reviewed. Three principles, namely, neutrality principle, stoichiometrical principle and coordination principle were proposed for building up cluster models of metal oxides. od correlation between the topologic parameters Nc(βc), Na(βa) and Nd(βd) with the stability of clusters has been shown. The problem of how the ways of embedding affect the calculated electronic properties of the substrate clusters and the adsorption properties has been investigated. Based on these, we proposed an SPC model, which is a stoichiometric cutout cluster embedded in a spherically expanded point charge surrounding with charges being self-consistently determined. We have successfully applied the SPC model to a variety of important systems, including H2/ZnO, O/M , NO/M , N2O/M , N2O/Li/M , CO/M and CO/NiO.
2004, 20(08S): 1055-1062
doi: 10.3866/PKU.WHXB200408zk24
Abstract:
Chemistry in strong laser fields is a new research field in which dissociation of molecules in the intense laser field is a current topic of interest. Our results, including the theoretical model of field-assisted dissociation (FAD) and the experimental investigations on the dissociation of CH4 and CH3COCH3 in the intense femtosecond laser field are presented. Some assumptions are made in the model. When a laser field applies to a molecule, only the change of the one bond length, which lies along with the laser field, is taken into account and the rest of the molecular geometry is fixed. In addition, only molecular ions in the ground electronic state are considered. Ab initio potential energy surfaces in the external fields indicate that chemical bond tends to dissociate. QCT (quasi-classical trajectory) calculations clearly show the processes of bond breaking. It was found that the calculations based on the theoretical model are in excellent agreement with the experiment data.
Chemistry in strong laser fields is a new research field in which dissociation of molecules in the intense laser field is a current topic of interest. Our results, including the theoretical model of field-assisted dissociation (FAD) and the experimental investigations on the dissociation of CH4 and CH3COCH3 in the intense femtosecond laser field are presented. Some assumptions are made in the model. When a laser field applies to a molecule, only the change of the one bond length, which lies along with the laser field, is taken into account and the rest of the molecular geometry is fixed. In addition, only molecular ions in the ground electronic state are considered. Ab initio potential energy surfaces in the external fields indicate that chemical bond tends to dissociate. QCT (quasi-classical trajectory) calculations clearly show the processes of bond breaking. It was found that the calculations based on the theoretical model are in excellent agreement with the experiment data.
