Photodissociation of Cr(CO)6 in a molecular beam at 248 nm: Observation of primary and secondary photoproducts by mass spectrometry

Photodissociation of Cr(CO)6 induced by a KrF* excimer laser (248 nm) was examined under molecular beam conditions, using a quadrupole mass spectrometer with electron impact ionization (11--19 eV) to detect the products as their respective ions. The ions of all Cr(CO)x products (x=0--5) were produced upon photodissociation of Cr(CO)6 at laser fluences from 1 to 10 mJ cm-2. The quantitative behavior of the Cr(CO)+x product ion yields vs laser fluence as well as statistical rate calculations indicate that Cr(CO)4 is the major product formed upon single-photon dissociation of Cr(CO)6 under collisionless conditions at 248 nm. The additional Cr(CO)+x (x<4) product ions observed at low fluences are formed primarily by electron-impact fragmentation of Cr(CO)4 in the mass spectrometer ionizer. At laser fluences approx gt 5 mJ cm-2, secondary photodissociation of Cr(CO)4 becomes important. Cr(CO)2 is assigned as the major photoproduct formed via secondary photodissociation of Cr(CO)4