Electron impact and multiphoton ionization and fragmentation of molybdenum-cyclopentadienyl-dicarbonyl-nitrosyl at 351, 248 and 193 nm

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Electron impact (EI) and multiphoton ionization (MPI) mass spectra of CpMo(CO) 2NO (Cp  C 5H 5, cyclopentadienyl ligand) are reported. The ionization energy (8.20 eV) and appearance energies of major fragment ions are determined. Ion dissociation energies and formation enthalpies are derived from these data. On EI ionization molecular ions and large fragment ions are formed. A primary loss of CO ligands from molecular ions is favoured over NO or Cp elimination. Mo + ions are generated in low abundance only. On multiphoton excitation at the excimer laser wavelengths 351 and 248 nm and low laser intensities MoO + ions and, with lower abundance, Mo + ions are detected. At increasing laser intensities Mo + ions are becoming predominant. At 193 nm and low laser intensities CpMoNO + and CpMo + ions are formed. At higher laser intensities an increasing yield of smaller ions, particularly Mo +, are found. The number of absorbed photons for the formation of prominent ions is determined 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 intermediate molecular ionization and subsequent fragmentation.