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Green IX, Tang W, Neurock M, Yates JT. Spectroscopic Observation of Dual Catalytic Sites During Oxidation of CO on a Au/TiO2 Catalyst. Science 2011; 333:736-9. [DOI: 10.1126/science.1207272] [Citation(s) in RCA: 815] [Impact Index Per Article: 62.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Rajappan M, Yuan C, Yates JT. Lyman-α driven molecule formation on SiO2 surfaces—connection to astrochemistry on dust grains in the interstellar medium. J Chem Phys 2011; 134:064315. [DOI: 10.1063/1.3532089] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Voznyy O, Dubowski JJ, Yates JT, Maksymovych P. The role of gold adatoms and stereochemistry in self-assembly of methylthiolate on Au(111). J Am Chem Soc 2010; 131:12989-93. [PMID: 19737018 DOI: 10.1021/ja902629y] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
On the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new finding is that the building block of all these structures has the same stoichiometry of two thiolate species joined by a gold adatom. The self-arrangement of the methylthiolate-adatom complexes on the surface depends critically on their stereochemical properties. Variations of the latter can produce local ordering of adatom complexes with either (3 x 4) or (3 x 4 square root(3)) periodicity. A possible structural connection between the (3 x 4 square root(3)) structure and commonly observed (square root(3) x square root(3))R30 degrees phase in methylthiolate self-assembled monolayers is developed by taking into account the reduction in the long-range order and stereochemical isomerization at high coverage. We also suggest how the observed self-arrangements of methylthiolate may be related to the c(4 x 2) phase of its longer homologues.
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Affiliation(s)
- Oleksandr Voznyy
- Department of Electrical and Computer Engineering, Centre of Excellence for Information Engineering (CEGI), Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada.
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Berger T, Sterrer M, Diwald O, Knözinger E, Panayotov D, Thompson TL, Yates JT. Light-induced charge separation in anatase TiO2 particles. J Phys Chem B 2007; 109:6061-8. [PMID: 16851666 DOI: 10.1021/jp0404293] [Citation(s) in RCA: 277] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ultraviolet light-induced electron-hole pair excitations in anatase TiO(2) powders were studied by a combination of electron paramagnetic resonance and infrared spectroscopy measurements. During continuous UV irradiation in the mW.cm(-2) range, photogenerated electrons are either trapped at localized sites, giving paramagnetic Ti(3+) centers, or remain in the conduction band as EPR silent species which may be observed by their IR absorption. Using low temperatures (90 K) to reduce the rate of the electron-hole recombination processes, trapped electrons and conduction band electrons exhibit lifetimes of hours. The EPR-detected holes produced by photoexcitation are O(-) species, produced from lattice O(2-) ions. It is found that under high vacuum conditions, the major fraction of photoexcited electrons remains in the conduction band. At 298 K, all stable hole and electron states are lost from TiO(2). Defect sites produced by oxygen removal during annealing of anatase TiO(2) are found to produce a Ti(3+) EPR spectrum identical to that of trapped electrons, which originate from photoexcitation of oxidized TiO(2). Efficient electron scavenging by adsorbed O(2) at 140 K is found to produce two long-lived O(2)(-) surface species associated with different cation surface sites. Reduced TiO(2), produced by annealing in vacuum, has been shown to be less efficient in hole trapping than oxidized TiO(2).
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Affiliation(s)
- T Berger
- Institut für Materialchemie, Technical University of Vienna, A-1210 Vienna, Austria
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Dougherty DB, Maksymovych P, Lee J, Yates JT. Local spectroscopy of image-potential-derived states: from single molecules to monolayers of benzene on Cu(111). Phys Rev Lett 2006; 97:236806. [PMID: 17280227 DOI: 10.1103/physrevlett.97.236806] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Indexed: 05/13/2023]
Abstract
Stark-shifted image-potential states were measured with an STM tip for benzene adsorbed on a Cu(111) surface. A single benzene molecule locally shifts the position of the first image state toward the Fermi level by 0.2 eV relative to its position on the clean surface. The energetic position of this molecule-modified state shifts to lower energy with increasing coverage of benzene on the surface. This is attributed to local surface potential changes that are correlated with the lowering of the crystal work function due to adsorption of benzene.
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Affiliation(s)
- D B Dougherty
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Abstract
Adsorption structures of the dibenzo[a,j]coronene (C(32)H(16)) molecule on the clean Si(001)-2 X 1 surface were investigated by scanning tunneling microscopy (STM) in conjunction with electronic structure calculations. The dibenzo[a,j]coronene molecules were found to adsorb on three different sites: one major adsorption site and two minor adsorption sites. The formation of four to eight Si-C covalent bonds is responsible for the different surface bonding structures observed. Bond strain effects due to out-of-plane bending of the molecule play a significant role in governing the surface bond energies. The geometries of the three adsorption sites were established by comparison of the experimental and simulated STM images. By applying an electrical pulse, the molecule can be made to hop from one site to another site without breaking the dibenzo[a,j]coronene molecular structure.
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Affiliation(s)
- T Suzuki
- Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Dougherty DB, Lee J, Yates JT. Role of Conformation in the Electronic Properties of Chemisorbed Pyridine on Cu(110): An STM/STS Study. J Phys Chem B 2006; 110:11991-6. [PMID: 16800507 DOI: 10.1021/jp060733r] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Pyridine was chemisorbed on Cu(110) at 10 K and observed using STM at 5 K as dosed and after annealing to temperatures between 20 and 300 K. At very low coverage, two molecular species with different apparent heights are observed to coexist. The higher species is assigned to a pyridine molecule bonded with its symmetry axis perpendicular to the surface plane, while the lower species is assigned to a pyridine molecule that is tilted down toward the surface plane. At low coverage, the tilted pyridine species predominates on the surface, but as the total surface coverage of pyridine increases, the molecules stand up until the upright geometry becomes favored. Measurements of the STS of the two species show different molecular resonances derived from the lowest unoccupied pyridine pi* orbitals. The tilted pyridine species has a peak in the unoccupied local density of states at 2.6 +/- 0.1 eV, whereas the upright pyridine species has a peak at 2.3 +/- 0.1 eV.
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Affiliation(s)
- D B Dougherty
- Surface Science Center and Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Suzuki T, Levy J, Yates JT. Localized deposition of coronene molecules on Si(001)-2x1 using a scanning tunneling microscope tip source. Nano Lett 2006; 6:138-43. [PMID: 16402802 DOI: 10.1021/nl0519635] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The deposition of coronene molecules from scanning tunneling microscope (STM) tips onto a clean Si(001)-2x1 surface at 25 degrees C was investigated. The STM tips, contaminated with coronene, were found to deposit coronene molecules on the clean Si(001) surface, allowing patterns to be generated. Covalent Si-C chemical bonds, formed between the coronene molecules and the Si substrate, froze the flip-flop motion of the adjacent Si-Si dimers on the substrate. In most cases, the mode of coronene bonding to Si(001) is independent of whether deposition occurs from the gas phase or from the STM tip. Despite the covalent chemical bonds formed between the coronene molecule and the Si substrate, the STM tip can drag the coronene laterally on the Si substrate without inducing a chemical change in the molecule. Sharp spikes observed in the tunneling current during the coronene deposition reflect the abrupt decrease of the tip-substrate distance at the instant of transport of the molecule from tip to surface.
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Affiliation(s)
- T Suzuki
- Surface Science Center, Department of Chemistry, University of Pittsburgh, Pennsylvania 15260, USA
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Panayotov D, Kondratyuk P, Yates JT. Photooxidation of a mustard gas simulant over TiO2-SiO2 mixed-oxide photocatalyst: site poisoning by oxidation products and reactivation. Langmuir 2004; 20:3674-8. [PMID: 15875398 DOI: 10.1021/la0303815] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The photooxidation of 2-chloroethyl ethyl sulfide (2-CEES), a simulant for mustard gas, was studied using transmission IR spectroscopy on a mixed-oxide TiO2-SiO2 photocatalyst. Ultraviolet irradiation in the photon energy range from 2.1 to 5 eV was employed at a catalyst temperature of 200 K. Rapid photooxidation was observed by the loss of infrared intensity in the v(CHx) stretching region, and concomitant infrared features of adsorbed oxidation products were observed to develop. The oxidation products, captured on the photocatalyst at 200 K, were found to block 2-CEES readsorption. Upon heating the poisoned photocatalyst to about 300 K, infrared measurements indicate that the adsorbed CO2 oxidation product was desorbed. The capability for full readsorption of 2-CEES was achieved upon heating the poisoned photocatalyst to 397 K, and continued rapid photooxidation of the 2-CEES was then possible at about 1/3 the rate found for the fresh catalyst. Thus thermal treatment at 397 K of oxidation-product-poisoned TiO2-SiO2 material is able to partially restore the TiO2-SiO2 photooxidation activity.
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Affiliation(s)
- D Panayotov
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Affiliation(s)
- D. Panayotov
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - J. T. Yates
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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Affiliation(s)
- D. Panayotov
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - J. T. Yates
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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Affiliation(s)
- D. A. Panayotov
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - D. K. Paul
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - J. T. Yates
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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Byl O, Kondratyuk P, Yates JT. Adsorption and Dimerization of NO Inside Single-Walled Carbon NanotubesAn Infrared Spectroscopic Study. J Phys Chem B 2003. [DOI: 10.1021/jp022565i] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- O. Byl
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - P. Kondratyuk
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - J. T. Yates
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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Balldin UI, Derefeldt G, Eriksson L, Werchan PM, Andersson P, Yates JT. Color vision with rapid-onset acceleration. Aviat Space Environ Med 2003; 74:29-36. [PMID: 12546296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/28/2023]
Abstract
INTRODUCTION Only sporadic information exists concerning perceived color shifts at increased G-loads. The purpose of this study was to investigate whether or not color vision is affected by rapid onset high G7-loads up to +9 Gz, and specifically whether perception of hue changes. METHODS There were 10 male subjects, 9 with normal color vision and 1 with red-green protanomaly, all accustomed to Gz-loads in a human centrifuge. Each subject was tested on a total of 60 Gz-exposures with 10 s periods at +3, +5, +7, and +9 Gz in the centrifuge on three different days. G-onset rate was 6 G x s(-1). The subjects wore an anti-G suit and performed straining maneuvers if necessary to maintain vision. Five square color stimuli of medium saturation (yellow, red, blue, green, and gray) were projected one at a time on a screen in front of the subject, who gave his hue response orally. RESULTS In 96.6% of exposures to various Gz-loads, the subjects responded by correctly naming colors. (The statistical analyses of the results were done for the subjects with normal color vision, with the protanomalous subject excluded.) Hue shifts occurred at the higher +Gz-levels, including 7.7% of the +9 Gz exposures. Yellow was the hue most frequently perceived as changed. Hue shifts were reported for yellow in 11% and 16% of the +7 and +9 Gz exposures, respectively. Hue shifts at +9 Gz occurred as frequently as blackout and G-LOC together. However, statistical analyses showed no significant effects for +Gz-load. CONCLUSIONS Absolute identification of the color stimuli of medium saturation was stable and was not significantly affected by the rapid onset +Gz-loads up to and including +9 Gz.
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Affiliation(s)
- U I Balldin
- FOI, Swedish Defence Research Agency, formerly National Defence Research Establishment, FOA, Sweden.
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Abstract
We show that the electrostatic charging of an aluminum oxide film by electron-bombardment produces a greatly enhanced rate of Al(111) oxidation by O2(g) at 90 K, compared to a film which has not been bombarded by electrons. This novel memory effect for prior electron irradiation is caused by the negative electrostatic potential created and stored on the outer oxide film surface as a result of electron bombardment. The high electrostatic field ( approximately 10(7) V/cm) produced across the depth of the film is postulated to cause an enhancement of ion migration through the film, leading to rapid oxide film growth, as predicted by the Cabrera-Mott theory of low temperature metal oxidation.
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Affiliation(s)
- I Popova
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pittsburgh, PA 15260, USA
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Lee JG, Ahner J, Yates JT. Adsorption Geometry of 4-Picoline Chemisorbed on the Cu(110) Surface: A Study of Forces Controlling Molecular Self-Assembly [ J. Am. Chem. Soc. 2002, 124, 2772−2780]. J Am Chem Soc 2002. [DOI: 10.1021/ja025113s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Cheng CC, Lucas SR, Gutleben H, Choyke WJ, Yates JT. Atomic hydrogen-driven halogen extraction from silicon(100): Eley-Rideal surface kinetics. J Am Chem Soc 2002. [DOI: 10.1021/ja00030a020] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Guo X, Yoshinobu J, Yates JT. Decomposition of an organophosphonate compound (dimethylmethylphosphonate) on the nickel(111) and palladium(111) surfaces. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100380a054] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Linsebigler AL, Smentkowski VS, Ellison MD, Yates JT. Interaction of chlorine with iron(110) in the temperature range 90-1050 K. J Am Chem Soc 2002. [DOI: 10.1021/ja00028a011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Basu P, Yates JT. Carbon-hydrogen bond lability in adsorbed hydrocarbon layers: butadiene-derived species on rhodium/alumina. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100353a032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Basu P, Panayotov D, Yates JT. Spectroscopic evidence for the involvement of hydroxyl groups in the formation of dicarbonylrhodium(I) on metal oxide supports. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100296a007] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Smentkowski VS, Hagans P, Yates JT. Study of the catalytic destruction of dimethyl methylphosphonate(DMMP): oxidation over molybdenum(110). ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100333a034] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Guo X, Hanley L, Yates JT. Thermal stability of the carbon-oxygen bond of methanol on the palladium(111) surface: an isotopic mixing study. J Am Chem Soc 2002. [DOI: 10.1021/ja00191a007] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Colaianni ML, Chen JG, Weinberg WH, Yates JT. The adsorption and dissociation of carbon monoxide on clean and oxygen-modified molybdenum(110) surfaces. J Am Chem Soc 2002. [DOI: 10.1021/ja00036a024] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Guo X, Hoffman A, Yates JT. Hydrogen cyanide adsorption on the palladium(111) surface: surface temperature and coverage dependence. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100347a068] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Heiz U, Sherwood R, Cox DM, Kaldor A, Yates JT. CO Chemisorption on Monodispersed Platinum Clusters on SiO2: Detection of CO Chemisorption on Single Platinum Atoms. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100021a044] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Chen JG, Beebe TP, Crowell JE, Yates JT. Reaction of atomically clean aluminum and chemically modified aluminum with alkyl halides. J Am Chem Soc 2002. [DOI: 10.1021/ja00240a021] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Hagans PL, Chorkendorff I, Yates JT. Scanning kinetic spectroscopy and temperature-programmed desorption studies of the adsorption and decomposition of hydrogen cyanide on the nickel(111) surface. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100313a045] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Yates JT, Garland CW. INFRARED STUDIES OF CARBON MONOXIDE CHEMISORBED ON NICKEL AND ON MERCURY-POISONED NICKEL SURFACES1. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100822a007] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Taylor PA, Wallace RM, Cheng CC, Weinberg WH, Dresser MJ, Choyke WJ, Yates JT. Adsorption and decomposition of acetylene on silicon(100)-(2.times.1). J Am Chem Soc 2002. [DOI: 10.1021/ja00043a020] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Chen JG, Crowell JE, Ng L, Basu P, Yates JT. Dissociative chemisorption of carbon monoxide on nickel films promoted by aluminum: detection of a precursor state to carbon monoxide dissociation by Electron Energy Loss Spectroscopy. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100320a035] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Lee JG, Ahner J, Yates JT. Adsorption geometry of 4-picoline chemisorbed on the Cu(110) surface: a study of forces controlling molecular self-assembly. J Am Chem Soc 2002; 124:2772-80. [PMID: 11890829 DOI: 10.1021/ja011898a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The adsorption of 4-picoline (4-methylpyridine) on the Cu(110) surface has been studied with time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) and other methods. Using deuterium labeling in the methyl group and hydrogen labeling on the aromatic ring, it has been possible to separately monitor by TOF-ESDIAD the C-D bond directions and the C-H bond directions in the adsorbed molecule. These triangulation measurements have led to a detailed understanding of the conformation of the adsorbed molecule relative to the Cu(110) crystal lattice, allowing one to witness changes in the molecular conformation as adsorbate-adsorbate interactional effects take place for increasing coverages. At low coverages, the molecule adsorbs by the N atom at an atop Cu site with the aromatic ring parallel to the <001> azimuth and with the molecular axis inclined 33 (+/- 5) degrees along the <001> azimuth. As rows of 4-picoline molecules form long range ordered chain structures oriented along the <112> azimuth, the aromatic ring twists 29 degrees about the inclined molecular axis as a result of forces between the adsorbate molecules. The initial tilting of the molecular axis at low coverage is likely due to the interaction of the positive-outward dipole with its image in the substrate. The ring twist may result from dipoleminus signdipole forces between the adsorbate molecules in the rows formed tending to form nested parallel pyridine rings. These studies are the first to apply the TOF-ESDIAD method for the measurement of the direction of chemical bonds at more than one molecular location within an adsorbed molecule and the new method is named electron stimulated desorption-molecular triangulation (ESD-MT). The results obtained give information of importance in understanding the factors which control conformational effects during the molecular self-assembly of complex adsorbed molecules on surfaces.
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Affiliation(s)
- J-G Lee
- Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
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Kuznetsova A, Popova I, Yates JT, Bronikowski MJ, Huffman CB, Liu J, Smalley RE, Hwu HH, Chen JG. Oxygen-containing functional groups on single-wall carbon nanotubes: NEXAFS and vibrational spectroscopic studies. J Am Chem Soc 2001; 123:10699-704. [PMID: 11674002 DOI: 10.1021/ja011021b] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Single-walled nanotubes (SWNTs) produced by plasma laser vaporization (PLV) and containing oxidized surface functional groups have been studied for the first time with NEXAFS. Comparisons are made to SWNTs made by catalytic synthesis over Fe particles in high-pressure CO, called HiPco material. The results indicate that the acid purification and cutting of single-walled nanotubes with either HNO3/H2SO4 or H2O2/H2SO4 mixtures produces the oxidized groups (O/C = 5.5-6.7%), which exhibit both pi*(CO) and sigma*(CO) C K-edge NEXAFS resonances. This indicates that both carbonyl (C=O) and ether C-O-C functionalities are present. Upon heating in a vacuum to 500-600 K, the pi*(CO) resonances are observed to decrease in intensity; on heating to 1073 K, the sigma*(CO) resonances disappear as the C-O-C functional groups are decomposed. Raman spectral measurements indicate that the basic tubular structure of the SWNTs is not perturbed by heating to 1073 K, based on the invariance of the ring breathing modes upon heating. The NEXAFS studies agree well with infrared studies which show that carboxylic acid groups are thermally destroyed first, followed by the more difficult destruction of ether and quinone groups. Single-walled nanotubes produced by the HiPco process, and not treated with oxidizing acids, exhibit an O/C ratio of 1.9% and do not exhibit either pi*(CO) or sigma*(CO) resonances at the detection limit of NEXAFS. It is shown that heating (to 1073 K) of the PLV-SWNTs containing the functional groups produces C K-edge NEXAFS spectra very similar to those seen for the HiPco material. The NEXAFS spectra are calibrated against spectra measured for a number of fused-ring aromatic hydrocarbon molecules containing various types of oxidized functional groups present on the oxidized SWNTs.
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Affiliation(s)
- A Kuznetsova
- Department of Chemistry, Surface Science Center, University of Pittsburgh, Pennsylvania 15260, USA
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Kuznetsova A, Yates JT, Simonyan VV, Johnson JK, Huffman CB, Smalley RE. Optimization of Xe adsorption kinetics in single walled carbon nanotubes. J Chem Phys 2001. [DOI: 10.1063/1.1395057] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Lee JG, Ahner J, Yates JT. Erratum: “The adsorption conformation of chemisorbed pyridine on the Cu(110) surface” [J. Chem. Phys. 114, 1414 (2001)]. J Chem Phys 2001. [DOI: 10.1063/1.1368661] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Burns JW, Ivan DJ, Stern CH, Patterson JC, Johnson PC, Drew WE, Yates JT. Protection to +12 Gz. Aviat Space Environ Med 2001; 72:413-21. [PMID: 11346005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Abstract
BACKGROUND The U.S. Air Force has developed +Gz-protective equipment that will provide most pilots protection to +9 Gz with minimal-to-no straining. This equipment includes a pressure breathing system called COMBAT EDGE (CE), which is currently operational, and the Advanced Technology Anti-G Suit (ATAGS), which is not yet operational. For future high-performance aircraft design it is important to know the upper limit of various protective equipment and techniques. METHODS Six subjects were randomly exposed to a 12-cell matrix composed of +Gz and the following combinations of protective equipment at three seat-back angles (13 degrees, 30 degrees and 55 degrees from the vertical): 1) the standard CSU-13B/P anti-G suit (STD); 2) the STD suit with CE; 3) the ATAGS; and 4) the ATAGS with CE. Relaxed, followed by straining +Gz tolerance was determined using 15-s rapid onset runs to a maximum of +12 Gz. A comprehensive battery of baseline and post-exposure medical surveillance studies was performed to evaluate the medical consequences of these high +Gz exposures. RESULTS All 6 subjects were able to achieve +12 Gz with various combinations of +Gz-protective equipment, seat-back angle, and various amounts of straining, from none to maximum. When the data were collapsed over all protective equipment there was a significant (p < 0.05) seat effect. Relaxed tolerance to ROR increased with seat-back angle from 13 degrees to 30 degrees to 55 degrees. There was also a significant protective equipment effect when the data were collapsed over all seat-back angles. CONCLUSIONS These data confirm that effortless protection to +9 Gz is available using ATAGS/CE with the 13 degree and 30 degree seat-back angle (F-15, F-16 and F-22) and to +10.5 Gz with a 55 degree seat-back angle. Moreover, with ATAGS/CE, and a moderate degree of straining, +12 Gz is definitely achievable at 55 degrees, even with reduced anti-G suit pressure at 55 degrees. With additional straining +12 GC is also achievable at the 13 degree and 30 degree seat-back angles.
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Affiliation(s)
- J W Burns
- School of Aerospace Medicine, Brooks AFB, TX, USA
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Affiliation(s)
- C. N. Rusu
- Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - J. T. Yates
- Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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