ELECTRON-IMPACT AND MULTIPHOTON IONIZATION AND FRAGMENTATION OF DICARBONYL CYCLOPENTADIENYL METHYL IRON AND PENTAMETHYLCYCLOPENTADIENYL DICARBONYL METHYL IRON

Electron impact (EI) and multiphoton ionization (MPI) mass spectra of the title compounds CpFe(CO)(2)CH3 (1) and CpFe(CO)(2)CH3 (2) are rep orted. Under EI molecular ions and large fragment ions are formed from both compounds. Direct analysis of metastable ions showed that succes sive detachments of ligands from 1 lead to Fe+ ions while loss of Fe a toms is more important for ionic fragments of 2. Ionization energies o f 7.56 eV (1) and 7.25 eV (2) were determined by extrapolating ion abu ndances versus energy in semi-log plots. In the same way, appearance e nergies of major fragment ions were obtained for both compounds. Deriv ed data include ion dissociation energies and enthalpies of ion format ion. Typically, the dissociation energies required were below 1 eV for splitting off CO ligands and above 2 eV for CH3 detachment. Upon MPI of both compounds at the excimer wavelengths 351, 308 and 248 nm Fe+ i ons are formed almost exclusively, probably by breakdown of the neutra l parent compounds yielding bare metal atoms that are subsequently ion ized. At 193 nm, molecular ions appear and large fragment ions are gen erated with low abundance, depending on laser intensity. High laser in tensities lead to complete breakdown and Fe+ ion formation. At low int ensities loss of Fe atoms is observed only in the case of 2. A depende nce on pressure was observed for abundances of molecular ions and some fragment ions of 2. The abundances of C10H13+ and of Fe+ ions are ind ependent of pressure.