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- Gustafsson, Kristian, 1972
(författare)
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Infrared spectroscopy of O2 and N2 adsorption on the clean and hydrogen covered Pt(111) surface
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the investigation of O2and N2 adsorption on the clean and the hydrogen covered Pt(111) surface. Using infrared reflection absorption spectroscopy (IRAS) both physisorbed and chemisorbed molecular adsorptionstates have been identified and characterized via theircharacteristic internal vibration spectra.On Pt(111) the IRAS measurements reveal a physisorbed O2 state at temperatures below 40 K while O2 chemisorption in peroxo- and superoxo-like states are observed in the investigatedtemperature range 30-90 K. The temperature dependence of theO2 chemisorption probability and the thermal conversion of physisorbed 2 into primarily the superoxo state show that the physisorbed state acts as a precursor to the O2chemisorption.On the hydrogen saturated Pt(111)(1x1)H surface no O2 chemisorption occurs and the physisorbed molecules do not act as precursors to chemisorption but simply desorb at temperatures above 45 K. When the Pt(111) surface is partially covered with p(1x1)H islands, O2 chemisorption in the peroxo and superoxostate occur on the bare Pt(111) regions. However, the thermal activation of the O2 precursor is altered presumably due to loss of trapped precursor molecules by thermal desorption from thechemically inert p(1x1)H islands.N2 adsorption on Pt(111) at 30 K involve, apart from a weak defect related signal, two N2 states, one chemisorbed and one physisorbed. Almost identical uptake behavior in these two statesindicates that they are intrinsic constituents of the growing (3x3) ordered nitrogen islands, and that there is at least one chemisorbed molecule in the (3x3) unit cell. The hydrogen saturated Pt(111)(1x1)H surface is inert with respect to N2 chemisorption but below 45 K N2 physisorbs and at 30 K a commensurate (3x3) ordered N2 adlayer forms.The infrared absorbance and the polarization induced dynamicdipole moments related to the fundamental internal vibrationtransition of N2 and O2 physisorbed on the chemically inert Pt(111)(1x1)H surface have been analyzed together with the induced static dipole moments derived from work function data. A good estimate of the induced dynamic as well as static dipole moments can in general be obtained from a van der Waals model.
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- Gustafsson, Kristian, 1972, et al.
(författare)
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Infrared spectroscopy of physisorbed and chemisorbed N-2 in the Pt(111)(3x3)N-2 structure
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:19
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Tidskriftsartikel (refereegranskat)abstract
- Using infrared spectroscopy and low electron energy diffraction, we have investigated the adsorption of N-2, at 30 K, on the Pt(111) and the Pt(111)(1x1)H surfaces. At monolayer coverage, N-2 orders in commensurate (3x3) structures on both surfaces, and we propose that the unit cells contain four molecules in each case. The infrared spectra reveal that N-2 exclusively physisorbs on the Pt(111)(1x1)H surface, while both physisorbed and chemisorbed N-2 is detected on the Pt(111) surface. Physisorbed N-2 is the majority species in the latter case, and the two adsorption states show an almost identical uptake behavior, which indicates that they are intrinsic constituents of the growing (3x3) N-2 islands. An analysis of the infrared absorbance data, based on a simple scaling concept suggested by density functional theory calculations, supports a model in which the (3x3) unit cell contains one chemisorbed molecule in end-on atop configuration and three physisorbed molecules. We note that a classic ''pinwheel'' structure on a hexagonal lattice, with the end-on chemisorbed N2 molecules acting as ''pins,'' is compatible with this composition. (C) 2007 American Institute of Physics.
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- Gustafsson, Kristian, 1972, et al.
(författare)
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Leakage of O2 Precursor Molecules from Inert Hydrogen Islands on a Pt(111) Surface
- 2006
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Ingår i: Physical Review Letters. ; 97:7
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Tidskriftsartikel (refereegranskat)abstract
- We have observed, using infrared spectroscopy, that the precursor-mediated O2 chemisorption on the clean and the partially hydrogen-covered Pt(111) surfaces exhibits opposite temperature dependencies above the temperature for stable O2 physisorption. While the chemisorption probability on the clean surface increases with increasing temperature due to thermal activation of the precursor, it decreases on the partially hydrogen-covered surface which we suggest is due to a general loss of the mobile precursor molecules by thermal desorption from chemically inert hydrogen islands.
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