A time-dependent non-adiabatic formulation is considered for chemical reactions. Basic algorithms are presented for the photodissociation of CH3I under the influence of strong short laser pulses. Detailed insight into the dynamics of this process is demonstrated. A time-dependent self-consistent field approach is suggested when many degrees of freedom have to be considered simultaneously. The derivation is based on a Liouville space description for which quantum and classical mechanics are treated on equal grounds. A multiconfiguration approach is formulated for explicitly including correlation due to splitting of the probability density and for non-adiabatic motion.
{"title":"Non-adiabatic reactive routes and the applicability of multiconfiguration time-dependent self-consistent field approximations","authors":"R. Kosloff, A. Hammerich","doi":"10.1039/DC9919100239","DOIUrl":"https://doi.org/10.1039/DC9919100239","url":null,"abstract":"A time-dependent non-adiabatic formulation is considered for chemical reactions. Basic algorithms are presented for the photodissociation of CH3I under the influence of strong short laser pulses. Detailed insight into the dynamics of this process is demonstrated. A time-dependent self-consistent field approach is suggested when many degrees of freedom have to be considered simultaneously. The derivation is based on a Liouville space description for which quantum and classical mechanics are treated on equal grounds. A multiconfiguration approach is formulated for explicitly including correlation due to splitting of the probability density and for non-adiabatic motion.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"9 1","pages":"239-247"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87770848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Katz, Jeunghee Park, S. Satyapal, Shintaro Tasaki, A. Chattopadhyay, W. Yi, R. Bersohn
The reaction H + SiD4→ D + SiH3D is found to have a much lower threshold than the corresponding exchange reaction of H with CD4. The D atom carries away most of the initial translational energy of the H atom. When the H-atom velocity distribution is anisotropic, the D-atom velocity distribution is anisotropic in the same sense. The exchange cross-sections for the reaction H + SiH3D are about one half of those for SiD4. All this evidence leads to the conclusion that the mechanism of the exchange is an inversion.
H + SiD4→D + SiH3D反应的阈值远低于H与CD4的相应交换反应。D原子带走了H原子的大部分初始平动能。当h原子的速度分布是各向异性时，d原子的速度分布也是各向异性。反应H + SiH3D的交换截面约为反应SiD4的一半。所有这些证据都得出这样的结论:这种交换的机制是一种反转。
{"title":"Exchange reactions of hydrogen atoms with SiD4: an inversion mechanism?","authors":"B. Katz, Jeunghee Park, S. Satyapal, Shintaro Tasaki, A. Chattopadhyay, W. Yi, R. Bersohn","doi":"10.1039/DC9919100073","DOIUrl":"https://doi.org/10.1039/DC9919100073","url":null,"abstract":"The reaction H + SiD4→ D + SiH3D is found to have a much lower threshold than the corresponding exchange reaction of H with CD4. The D atom carries away most of the initial translational energy of the H atom. When the H-atom velocity distribution is anisotropic, the D-atom velocity distribution is anisotropic in the same sense. The exchange cross-sections for the reaction H + SiH3D are about one half of those for SiD4. All this evidence leads to the conclusion that the mechanism of the exchange is an inversion.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"120 1","pages":"73-78"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77968910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent results on the ab initio potential-energy surface (PES) and dynamics calculations closely related to the experiments of ‘transition-state spectroscopy’(TSS) are discussed. The topics included are the photodissociations of NaI and ozone, and the unimolecular dissociation of FHF–. The non-adiabatic coupling in the ion–covalent crossing region of the NaI dissociation is calculated based on the CASSCF-MRCI method and compared with experimental and empirical estimates. The PESs of the ozone photodissociation are calculated using the CASSCF-SECI method. Characteristics of the ground and the excited B-state PESs are compared with the existing PESs. The weak structure seen in the Hartley band is explained in terms of transition-state dynamics based on three-dimensional quantum calculations using new PESs. The CEPA PES of the unimolecular dissociation of FHF– to the F–+ HF channel is calculated. Based on the quantum-mechanical variational calculation, the vibrationally highly excited FHF– anion above its dissociation threshold is suggested as a candidate of TSS of unimolecular dissociation reactions without a barrier.
{"title":"Ab initio molecular orbital and dynamics study of transition-state spectroscopy","authors":"K. Yamashita, K. Morokuma","doi":"10.1039/DC9919100047","DOIUrl":"https://doi.org/10.1039/DC9919100047","url":null,"abstract":"Recent results on the ab initio potential-energy surface (PES) and dynamics calculations closely related to the experiments of ‘transition-state spectroscopy’(TSS) are discussed. The topics included are the photodissociations of NaI and ozone, and the unimolecular dissociation of FHF–. The non-adiabatic coupling in the ion–covalent crossing region of the NaI dissociation is calculated based on the CASSCF-MRCI method and compared with experimental and empirical estimates. The PESs of the ozone photodissociation are calculated using the CASSCF-SECI method. Characteristics of the ground and the excited B-state PESs are compared with the existing PESs. The weak structure seen in the Hartley band is explained in terms of transition-state dynamics based on three-dimensional quantum calculations using new PESs. The CEPA PES of the unimolecular dissociation of FHF– to the F–+ HF channel is calculated. Based on the quantum-mechanical variational calculation, the vibrationally highly excited FHF– anion above its dissociation threshold is suggested as a candidate of TSS of unimolecular dissociation reactions without a barrier.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"44 1","pages":"47-61"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84785008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The activated dissociative adsorption of H2 and D2 on a clean Cu(110) and a Cu(110)-K(1 × 2) reconstructed surface has been studied using supersonic molecular beams. Enhanced sticking of H2 over D2 at any particular normal energy in the pure beam experiment on Cu(110) is interpreted as an indication of the importance of the vibrational coordinate in the dissociation dynamics. The relative contributions of vibrational and translational energy in accessing the barrier is separated in vibrationally hot, translationally cold seeded beams. Results for hydrogen are presented which indicate a translational onset for the first vibrationally excited state H2(v= 1) at 130 meV. This result is consistent with a theoretically predicted barrier to dissociation of ca. 700 meV which lies somewhat in the exit channel of a two-dimensional potential-energy surface (2D-PES). The effect of alkali-metal adsorption on the (1 × 2) reconstructed surface is shown to enhance hydrogen adsorption, increase the activation energy to desorption and reduce the activation energy to adsorption. This result is consistent with a reduction in the height of a late barrier caused by a deeper atomic potential in the ‘product’ region of the 2D-PES.
{"title":"Dynamics of hydrogen adsorption on clean and alkali-metal covered Cu(110)","authors":"B. Hayden, C. Lamont","doi":"10.1039/DC9919100415","DOIUrl":"https://doi.org/10.1039/DC9919100415","url":null,"abstract":"The activated dissociative adsorption of H2 and D2 on a clean Cu(110) and a Cu(110)-K(1 × 2) reconstructed surface has been studied using supersonic molecular beams. Enhanced sticking of H2 over D2 at any particular normal energy in the pure beam experiment on Cu(110) is interpreted as an indication of the importance of the vibrational coordinate in the dissociation dynamics. The relative contributions of vibrational and translational energy in accessing the barrier is separated in vibrationally hot, translationally cold seeded beams. Results for hydrogen are presented which indicate a translational onset for the first vibrationally excited state H2(v= 1) at 130 meV. This result is consistent with a theoretically predicted barrier to dissociation of ca. 700 meV which lies somewhat in the exit channel of a two-dimensional potential-energy surface (2D-PES). The effect of alkali-metal adsorption on the (1 × 2) reconstructed surface is shown to enhance hydrogen adsorption, increase the activation energy to desorption and reduce the activation energy to adsorption. This result is consistent with a reduction in the height of a late barrier caused by a deeper atomic potential in the ‘product’ region of the 2D-PES.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"64 1","pages":"415-423"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89174523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Measurements of the rotational state distributions for the H2 product of the H + RH → H2+ R reactions (RH = HCl, HBr, HI, CH4, C2H6, C3H8) at a collision energy of 1.6 eV are reported. For the reactions with the hydrogen halides we also have carried out quasiclassical trajectory calculations for conditions that mimic those of the experiments. We find that the rotational state distributions are quite characteristic and distinguishing in these systems. The combination of experiments and calculations allows us to provide some compelling explanation of how the structure and dynamics in the transition state are coupled to the product rotational state distributions. Not surprisingly, mere measurement of the rotational state distributions is insufficient to establish this connection, as illustrated by the results of the state-to-state experiments with the alkanes as reactants. These reactions give anomalous rotational state distributions, showing rotational excitation that actually increases with increasing product vibrational energy, rather than decreasing, as has been observed for all other reactions whose rotational and vibrational state distributions we know have been measured.
{"title":"Transition-state control of product rotational distributions in H + RH → H2+ R reactions (RH = HCl, HBr, HI, CH4, C2H6, C3H8)","authors":"J. Valentini, P. Aker, G. Germann, Y. Huh","doi":"10.1039/DC9919100173","DOIUrl":"https://doi.org/10.1039/DC9919100173","url":null,"abstract":"Measurements of the rotational state distributions for the H2 product of the H + RH → H2+ R reactions (RH = HCl, HBr, HI, CH4, C2H6, C3H8) at a collision energy of 1.6 eV are reported. For the reactions with the hydrogen halides we also have carried out quasiclassical trajectory calculations for conditions that mimic those of the experiments. We find that the rotational state distributions are quite characteristic and distinguishing in these systems. The combination of experiments and calculations allows us to provide some compelling explanation of how the structure and dynamics in the transition state are coupled to the product rotational state distributions. Not surprisingly, mere measurement of the rotational state distributions is insufficient to establish this connection, as illustrated by the results of the state-to-state experiments with the alkanes as reactants. These reactions give anomalous rotational state distributions, showing rotational excitation that actually increases with increasing product vibrational energy, rather than decreasing, as has been observed for all other reactions whose rotational and vibrational state distributions we know have been measured.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"10 1","pages":"173-182"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73806911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effect of resonances on the observable properties of chemical reactions is studied theoretically, in particular for I + HI → IH + I and Cl + HCl → ClH + Cl. All of our calculations use hyperspherical coordinates and accurate coupled-channel solutions to the Schrodinger equation for reactive scattering in three dimensions. For I + HI, we investigate the effect of potential surface variation on transition-state IHI– photodetachment spectra for total angular momentum quantum number equal to zero. Four different I + HI London–Eyring–Polanyi–Sato (LEPS) surfaces are used, with classical barrier heights varying from 0.048 to 0.243 eV. The low-energy portion of the photodetachment spectra are examined in detail; it is found that peaks in the spectra arising from resonances and from direct scattering move up and broaden in energy as the barrier height is increased. An approximate match of the theoretical peak widths and spacings with the experimental ones is obtained for one of the surfaces. However, the peak intensities differ, suggesting that LEPS surfaces may not be adequate to characterize fully the observed spectra. For Cl + HCl, we perform a centrifugal-sudden hyperspherical calculation in order to examine the scattering properties of the single isolated resonance with transition-state quantum numbers (ν1, ν2, ν3)=(0, 0, 2)(where ν1= symmetric stretching, v2= bending, V3= asymmetric stretching quantum numbers). This relatively narrow (width 4 meV) resonance produces substantial peaks in certain state resolved reaction probabilities, which leads to a smooth step-like behaviour in the integral cross-sections, and Breit–Wigner (or Lorentzian) peaks in the differential cross-sections. Simple dynamical models are developed which explain these results.
{"title":"Resonances in heavy + light–heavy atom reactions: influence on differential and integral cross-sections and on transition-state photodetachment spectra","authors":"G. Schatz, D. Sokolovski, J. Connor","doi":"10.1039/DC9919100017","DOIUrl":"https://doi.org/10.1039/DC9919100017","url":null,"abstract":"The effect of resonances on the observable properties of chemical reactions is studied theoretically, in particular for I + HI → IH + I and Cl + HCl → ClH + Cl. All of our calculations use hyperspherical coordinates and accurate coupled-channel solutions to the Schrodinger equation for reactive scattering in three dimensions. For I + HI, we investigate the effect of potential surface variation on transition-state IHI– photodetachment spectra for total angular momentum quantum number equal to zero. Four different I + HI London–Eyring–Polanyi–Sato (LEPS) surfaces are used, with classical barrier heights varying from 0.048 to 0.243 eV. The low-energy portion of the photodetachment spectra are examined in detail; it is found that peaks in the spectra arising from resonances and from direct scattering move up and broaden in energy as the barrier height is increased. An approximate match of the theoretical peak widths and spacings with the experimental ones is obtained for one of the surfaces. However, the peak intensities differ, suggesting that LEPS surfaces may not be adequate to characterize fully the observed spectra. For Cl + HCl, we perform a centrifugal-sudden hyperspherical calculation in order to examine the scattering properties of the single isolated resonance with transition-state quantum numbers (ν1, ν2, ν3)=(0, 0, 2)(where ν1= symmetric stretching, v2= bending, V3= asymmetric stretching quantum numbers). This relatively narrow (width 4 meV) resonance produces substantial peaks in certain state resolved reaction probabilities, which leads to a smooth step-like behaviour in the integral cross-sections, and Breit–Wigner (or Lorentzian) peaks in the differential cross-sections. Simple dynamical models are developed which explain these results.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"191 1","pages":"17-30"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76950628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. J. Maynard, A. D. Johnson, S. P. Daley, S. Ceyer
The absorption of atomic hydrogen on Ni(111) is observed to be induced by collisions with Ar, Kr or Xe atoms incident with energies in the normal direction greater than 60 kcal mol–1. The mechanism for collision-induced absorption involves momentary deformation of the lattice which opens channels leading to the bulk metal into which the hydrogen diffuses. The embedded hydrogen is detectable by high-resolution electron energy loss spectroscopy and is distinguishable from the vibrational modes of chemisorbed hydrogen on the basis of the dependence of the inelastically scattered electron intensity on electron impact energy. The embedded hydrogen has a vibrational frequency of 800–850 cm–1 and is observed to recombine and desorb as H2 between 180 and 220 K. Hydrogen absorption can also be achieved by exposure to atomic hydrogen. As much as an equivalent of 8 monolayers (ML) of hydrogen has been absorbed.
{"title":"A new mechanism for absorption: collision-induced absorption","authors":"K. J. Maynard, A. D. Johnson, S. P. Daley, S. Ceyer","doi":"10.1039/DC9919100437","DOIUrl":"https://doi.org/10.1039/DC9919100437","url":null,"abstract":"The absorption of atomic hydrogen on Ni(111) is observed to be induced by collisions with Ar, Kr or Xe atoms incident with energies in the normal direction greater than 60 kcal mol–1. The mechanism for collision-induced absorption involves momentary deformation of the lattice which opens channels leading to the bulk metal into which the hydrogen diffuses. The embedded hydrogen is detectable by high-resolution electron energy loss spectroscopy and is distinguishable from the vibrational modes of chemisorbed hydrogen on the basis of the dependence of the inelastically scattered electron intensity on electron impact energy. The embedded hydrogen has a vibrational frequency of 800–850 cm–1 and is observed to recombine and desorb as H2 between 180 and 220 K. Hydrogen absorption can also be achieved by exposure to atomic hydrogen. As much as an equivalent of 8 monolayers (ML) of hydrogen has been absorbed.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"91 1","pages":"437-449"},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89412362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Metallic glasses exhibit some unique properties which make them interesting materials in catalysis. Recently their use as catalyst precursors has been advanced and several efficient catalysts have been prepared by various pretreatments of the metallic glasses. An understanding of the solid-state reactions occurring during the transition of the amorphous precursor to the active catalyst was found to be crucial for successful application of these materials. This paper describes the present knowledge and discusses principal possibilities and problems involved in the application of metallic glasses in catalysis.
{"title":"Metallic glasses in heterogeneous catalysis","authors":"A. Baiker","doi":"10.1039/DC9898700239","DOIUrl":"https://doi.org/10.1039/DC9898700239","url":null,"abstract":"Metallic glasses exhibit some unique properties which make them interesting materials in catalysis. Recently their use as catalyst precursors has been advanced and several efficient catalysts have been prepared by various pretreatments of the metallic glasses. An understanding of the solid-state reactions occurring during the transition of the amorphous precursor to the active catalyst was found to be crucial for successful application of these materials. This paper describes the present knowledge and discusses principal possibilities and problems involved in the application of metallic glasses in catalysis.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"37 1","pages":"239-251"},"PeriodicalIF":0.0,"publicationDate":"1990-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80084948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Claesson, J. Eriksson, Christina E. Herder, B. Bergenståhl, E. Pezron, I. Pezron, P. Stenius
The nature of the repulsive forces acting between non-ionic hydrophilic surfaces has been investigated by the surface-force technique. For that purpose the interactions between head-groups of several non-ionic surfactants adsorbed on mica or hydrophobed mica were measured. In addition, the swelling pressure between monoglyceride layers in both the lamellar and the gel phases was determined using a water vapour pressure method. Repulsive short-range forces with an effective range of 1–3 nm were observed. They are believed to result from a combination of hydration and steric effects. The temperature dependence of the short-range force depends on the type of non-ionic group. When ethylene oxide or dimethylphosphine oxide groups are exposed towards the aqueous phase, an increased temperature results in a thicker layer, a steeper repulsive force, and a stronger attractive minimum. On the other hand, the layer thickness and the force acting between surfaces with exposed dimethylamine oxide groups are largely temperature independent, whereas in the case of monopalmitin, the force is more repulsive at higher temperatures. This behaviour is discussed with respect to the phase relations in the corresponding surfactant–water phase diagrams.
{"title":"Forces between non-ionic surfactant layers","authors":"P. Claesson, J. Eriksson, Christina E. Herder, B. Bergenståhl, E. Pezron, I. Pezron, P. Stenius","doi":"10.1039/DC9909000129","DOIUrl":"https://doi.org/10.1039/DC9909000129","url":null,"abstract":"The nature of the repulsive forces acting between non-ionic hydrophilic surfaces has been investigated by the surface-force technique. For that purpose the interactions between head-groups of several non-ionic surfactants adsorbed on mica or hydrophobed mica were measured. In addition, the swelling pressure between monoglyceride layers in both the lamellar and the gel phases was determined using a water vapour pressure method. Repulsive short-range forces with an effective range of 1–3 nm were observed. They are believed to result from a combination of hydration and steric effects. The temperature dependence of the short-range force depends on the type of non-ionic group. When ethylene oxide or dimethylphosphine oxide groups are exposed towards the aqueous phase, an increased temperature results in a thicker layer, a steeper repulsive force, and a stronger attractive minimum. On the other hand, the layer thickness and the force acting between surfaces with exposed dimethylamine oxide groups are largely temperature independent, whereas in the case of monopalmitin, the force is more repulsive at higher temperatures. This behaviour is discussed with respect to the phase relations in the corresponding surfactant–water phase diagrams.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"30 1","pages":"129-142"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75109012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Pizzini, K. Roberts, G. Greaves, N. Barrett, I. S. Dring, R. Oldman
The theoretical principles and instrumentation requirements of X-ray absorption spectroscopy under conditions of total external reflection are described with particular reference to their application in the characterisation of solid/solid interfaces. The advantages of combining XANES, EXAFS and reflectivity in a single series of measurements are highlighted through the structural characterisation of oxide layers on Cu and GaAs(100). The data reveal the surface of Cu deposited on float-glass to comprise a macroscopic mix of metallic Cu and structurally disordered oxide. The latter appears to have a local structure close to that observed in Cu2O but with a higher oxygen coordination at the surface. The surface of commercial-grade GaAs(100) has ca. 7–9 A of disordered oxide in which Ga coordinates to oxygen both tetrahedrally and octahedrally whilst As is only found in tetrahedral sites. Strong correlated second-shell cation coordinations around both Ga and As central atoms reveal a single non-stoichiometric surface oxide depleted of As at the surface. 10 and 100 A thick Cu films deposited on GaAs(100) are found to be completely oxidised with the oxide being more disordered and having a higher oxygen coordination than those deposited on float-glass. For 10 A thick films, Cu appears coordinated to Ga and As through the oxygen which decorates the inner surfaces of micro-voids and fissures in the disordered oxide on GaAs.
{"title":"X-Ray absorption spectroscopy under conditions of total external reflection: application to the structural characterisation of the Cu/GaAs(100) interface","authors":"S. Pizzini, K. Roberts, G. Greaves, N. Barrett, I. S. Dring, R. Oldman","doi":"10.1039/DC9908900051","DOIUrl":"https://doi.org/10.1039/DC9908900051","url":null,"abstract":"The theoretical principles and instrumentation requirements of X-ray absorption spectroscopy under conditions of total external reflection are described with particular reference to their application in the characterisation of solid/solid interfaces. The advantages of combining XANES, EXAFS and reflectivity in a single series of measurements are highlighted through the structural characterisation of oxide layers on Cu and GaAs(100). The data reveal the surface of Cu deposited on float-glass to comprise a macroscopic mix of metallic Cu and structurally disordered oxide. The latter appears to have a local structure close to that observed in Cu2O but with a higher oxygen coordination at the surface. The surface of commercial-grade GaAs(100) has ca. 7–9 A of disordered oxide in which Ga coordinates to oxygen both tetrahedrally and octahedrally whilst As is only found in tetrahedral sites. Strong correlated second-shell cation coordinations around both Ga and As central atoms reveal a single non-stoichiometric surface oxide depleted of As at the surface. 10 and 100 A thick Cu films deposited on GaAs(100) are found to be completely oxidised with the oxide being more disordered and having a higher oxygen coordination than those deposited on float-glass. For 10 A thick films, Cu appears coordinated to Ga and As through the oxygen which decorates the inner surfaces of micro-voids and fissures in the disordered oxide on GaAs.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"9 1","pages":"51-63"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87795523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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