Single-photon and multiphoton dissociation of molybdenum hexacarbonyl at 248 nm

Abstract

The one- and two-photon KrF*-laser photodissociation of Mo(CO)6 was studied in a molecular beam by using electron-impact ionization mass spectrometry to detect the photoproducts as their molecular ions. The predominant product ion observed following the one-photon dissociation of Mo(CO)6 is Mo(CO)5+. Mo(CO)4+ and Mo(CO)3+ are also observed. On the basis of the laser fluence dependence and electron energy dependence of the ion signals, we conclude that these ions derive predominantly from the ionization of Mo(CO)5, Mo(CO)4, and Mo(CO)3, respectively, which are formed in the single-photon dissociation of Mo(CO)6. At laser fluences greater than 5 mJ cm-2, secondary photodissociation processes produce a distribution of Mo(CO)x (x = 0-3) products, with the predominant two-photon product being Mo(CO)3. The formation of ground- and excited-state Mo atoms was further studied by emission spectroscopy. The a7S3 ground state of Mo is formed via a two-photon sequential mechanism, where a product of the single-photon dissociation of Mo(CO)6 acts as an intermediate. Formation of the excited states of Mo proceeds via an overall three-photon dissociation process. The Mo excited-state distribution formed is statistical, with a characteristic temperature of 11000 ± 2500 K. The formation of these excited states occur via a direct mechanism, where the parent hexacarbonyl absorbs three photons prior to dissociation. © 1991 American Chemical Society.