ELECTRON-IMPACT AND MULTIPHOTON IONIZATION AND FRAGMENTATION OF MOLYBDENUM-CYCLOPENTADIENYL-DICARBONYL-NITROSYL AT 351, 248 AND 193 NM

Electron impact (EI) and multiphoton ionization (MPI) mass spectra of CpMo(CO)(2)NO (Cp = C5H5, cyclopentadienyl ligand) are reported. The i onization energy (8.20 eV) and appearance energies of major fragment i ons are determined, Ion dissociation energies and formation enthalpies are derived from these data, On EI ionization molecular ions and larg e fragment ions are formed. A primary loss of CO ligands from molecula r ions is favoured over NO or Cp elimination. Mo+ ions are generated i n low abundance only. On multiphoton excitation at the excimer laser w avelengths 351 and 248 nm and low laser intensities MoO+ ions and, wit h lower abundance, Mo+ ions are detected, At increasing laser intensit ies Mo+ ions are becoming predominant. At 193 nm and low laser intensi ties CpMoNO+ and CpMo+ ions are formed, At higher laser intensities an increasing yield of smaller ions, particularly Mo+, are found, The nu mber of absorbed photons for the formation of prominent ions is determ ined and compared with EI appearance energies, The MPI results at 351 and 248 nm are interpreted with a dominant dissociation of the neutral parent compound followed by multiphoton ionization of the fragments, At 193 nm, however, a resonant multiphoton absorption leads to interme diate molecular ionization and subsequent fragmentation. (C) 1997 Else vier Science B.V.