MULTIPHOTON AND ELECTRON-IMPACT IONIZATION OF MANGANESE DECACARBONYL MN2(CO)10 AT 351-NM, 248-NM AND 193-NM - WAVELENGTH DEPENDENT COMPETITION BETWEEN IONIZATION AND DISSOCIATION

Multiphoton ionization and dissociation of Mn2(CO)10 is reported at 351, 248 and 193 nm in comparison with electron impact ionization. In the case of electron impact ionization. two decomposition pathways have been observed. The first is dominated by a fission of the metal-ligand bond and leads finally to the formation of the Mn2+ ion following successive elimination of all CO ligands. The second is characterized by a primary fission of the metal-metal bond. The remaining Mn(CO)5+ ions decay by successive elimination of CO to Mn+ metal ions. On multiphoton ionization at 351 nm the fragmentation pattern is governed by the Mn+ ion, formed after absorption of five photons. The primary cleavage of the Mn-Mn bond in the neutral parent molecule is dominant. Mn atoms are formed by elimination of CO ligands and ionized by subsequent absorption of further photons. Molecular ions and all fragment ions from the two decomposition pathways (except the missing MnCO+ ions) are observed with low yields. At 248 nm, Mn+ and Mn2+ ions, formed after absorption of four photons, are dominant. The fragmentation mechanism is characterized by dissociation of the neutral parent molecules to Mn atoms and Mn, dimers followed by ionization of these products after absorption of further photons. Molecular ions and Mn2(CO)5+ ions are also observed but formed by an ion/molecule reaction. At 193 nm. Mn2(CO)5+, Mn2+ and Mn+ ions are dominant. The first is formed after absorption of two photons, both metal ions after absorption of three photons. Molecular ions and all other fragment ions are observed with low yields. The multiphoton ionization/dissociation is characterized by dissociation preceding ionization at 351 and 248 nm and by ionization preceding dissociation at 193 nm.