Photochemistry of Mn2(CO)10 deposited on MgO thin films

Mn-2(CO)(10) deposits adsorbed at 90 K on MgO(100)/Mo(100) thin films are irradiated with laser light at a wavelength of 355 nm. Photoproducts are detected with mass spectrometry in combination with infra-red spectroscopy. The proposed main photolytic mechanism involves the absorption of 355-nm radiation by Mn-2(CO)(10) followed by CO detachment and dissociation. No manganese containing fragments are desorbed. Thermal desorption spectroscopy and Auger electron spectroscopy, performed after irradiation, show that at 500 K, the surface is still covered with 80-100% of the initial amount of manganese and 30-50% of the initial amount of carbon. This thermal stability for manganese indicates that laser-induced decarbonylation of the parent molecule leads to the creation of reactive fragments, which then bind to the MgO substrate. By contrast, the unirradiated Mn-2(CO)(10) desorbs readily on heating, and at 500 K, only about 5% of a monolayer of manganese remains on tie surface. (C) 1998 Elsevier Science B.V. All rights reserved.