Energetics of the Ionization and Dissociation of Ni(CO)4, Fe(CO)5, Cr(CO)6, Mo(CO)6 and W(CO)6

Abstract

The mass spectra of the metal carbonyls of Ni, Fe, Cr, Mo and W have been established. The ionization potentials and the energy necessary to form the various fragment ions have been measured. These data are used to calculate heats of formation for the various ions. The following dissociation energies were also calculated from the appearance potential data and ancillary thermochemical data and the valence state excitation energies: 1) specific bond dissociation energies for singly charged metal carbonyl ions, 2) average dissociation energies for singly charged parent ions, 3) average dissociation energies of neutral metal carbonyls to ground state products in which case comparison to calorimetric measurements are given, and 4) average dissociation energies of the metal carbonyls to valence state excited products. The unimolecular decomposition of metal carbonyls is discussed and the appearance potentials of the metal ions are used to calculate valence state excitation energies for the metal atoms. These values, W* = 3.18 eV, Mo* =4.92 eV, Cr* = 8.04 eV or 7.41 eV and Fe* = 6.57 eV are in excellent agreement with the observed spectroscopic values for Mo and with the values calculated from spectroscopic measurements of Cr and Fe. The value for the valence state excitation energy of W is the first reported in the literature.