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 ml 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 ≳ 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. © 1989 American Institute of Physics.