Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9595111 | Surface Science | 2005 | 8 Pages |
Abstract
In the present study, we investigated the mechanisms of state-selective fragment-ion desorption from condensed chlorobenzene following C 1s, Cl 2s, and Cl 2p core-level excitations by measuring the polarization dependences of NEXAFS (near-edge X-ray absorption fine structure) spectra recorded with desorbed ion yields and total electron yields (TEY). TEY-based NEXAFS shows no significant polarization dependence at any edges. In contrast, ion-based NEXAFS demonstrates a variety of marked polarization dependences. Cl 2p â 3d Ï* excitation induces a significant enhancement of Cl+ desorption yield at normal incidence (polarization â¥Â surface), while Cl 2s â Ï*(C-Cl) excitation stimulates a substantial enhancement of Cl+ desorption at grazing incidence (polarization â¥Â surface). C 1s â Ï*(C-Cl) enhances D+ desorption at grazing incidence, while C 1s â Ï*(CC) suppresses D+ desorption at all angles. All polarization dependences consistently reveal that excited molecules with upward-pointing bonds at top-most surfaces lead to efficient fragment desorption. This orientation effect is understood in terms of competing processes between the ultra-fast dissociation and charge-neutralization relaxation taking place during core-excited states. We demonstrate that the polarization-dependent ion-NEXAFS technique can distinguish direct state-specific fragmentation from indirect desorption caused by the collision of secondary electrons.
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Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
T. Sekiguchi, Y. Baba, I. Shimoyama, G. Wu, Y. Kitajima,