Thermal Chemistry and AdsorptionOrientation of 2-Fluoroethanol and 1,4-dioxane on Cu(100) Surface
| Autor: | Pei-Teng Chang, 張沛騰 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 Temperature-programmed reaction/desorption (TPD/R) and reflection absorption infrared spectroscopy (RAIRS) have been employed to investigate the thermal reactions and adsorption geometry of FCH2CH2OH and 1,4-dioxane molecules on clean and oxygen-preadsorbed Cu(100) surfaces. Molecular desorption predominates in heating FCH2CH2OH adsorbed on clean Cu(100). But ~20% adsorbed FCH2CH2OH molecules at about half monolayer coverage dissociate on the surface to form water, ethylene, and 1,4-dioxane. On the contrary, monolayer FCH2CH2OH completely dissociates on oxidized Cu(100) to form 1,4-dioxane and the surface intermediate of FCH2CH2O(a) which further decomposes to evolve FCH2CHO(g) at temperature higher than ~350 K. The decomposition of FCH2CH2OH to form FCH2CH2O(a) on oxidized Cu(100) begins at ~160 K and is completed prior to 220 K. On clean Cu(100), FCH2CH2OH molecules at ~0.25 monolayer coverage are adsorbed with the C-C-O skeleton approximately parallel to the surface. The C-C-O skeleton tilts away from the surface as the exposure is increased to a half monolayer coverage. However the parallel C-C-O orientation is not observed on the oxidized surface, even at the FCH2CH2OH exposure for a 0.25 monolayer coverage. 1,4-dioxane is adsorbed reversibly on the surface with monolayer desorption at 212 K and multilayer desorption at ∼165 K at 4 L exposure. Below ∼1.5 L exposure, i.e. 0.6 monolayer coverage, 1,4-dioxane molecules are adsorbed with the ring approximately parallel to the surface. C-H…Cu interaction is evidenced by the C-H vibrational mode softening of 2811 cm-1. Increasing 1,4-dioxane exposure leads to tilted geometry for some of the adsorbed molecules: ∼50% at a monolayer coverage at 110 K. However, the monolayer structure is not closely-packed at 110 K, most of the tilted molecules change to flat-lying geometry as the surface temperature is increased to 165 K just prior to the onset of molecular desorption. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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