Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5425724 | Surface Science | 2007 | 10 Pages |
The surface chemistry of proline is explored on Pd(1Â 1Â 1) using a combination of temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy. Proline adsorbs on Pd(1Â 1Â 1) at temperatures of 250Â K and below into second and subsequent layers prior to the saturation of the first layer, where approximately 70% of the adsorbed proline is present in its zwitterionic form. Molecular proline desorbs between â¼315Â K and â¼333Â K depending on coverage. When adsorbed at â¼300Â K, only the first monolayer is formed, and the proline is present as zwitterions, oriented such that all of the carbons are detected equally by XPS. Proline decomposes by scission of the C-COO bond, where the carboxylate moiety desorbs as carbon monoxide and carbon dioxide, while the nitrogen-containing moiety desorbs as to HCN, and evolves pyrrole at â¼390Â K, pyrrolidine at â¼410Â K, and final species that desorbs at â¼450Â K that cannot be unequivocally assigned but may be 2-butenenitrile (CH3-CHCH-CN), 3-butenenitrile (CH2CH-CH2-CN), 2-methyl-2-propenenitrile (CH2C(CH3)-CN) or cyclopropanecarbonitrile.