Mass spectra, ionisation potentials and related properties of metal-free and transition metal phthalocyanines

Abstract

The mass spectra and gaseous ionisation potentials of metal-free and a number of transition metal phthalocyanines have been determined by electron impact measurements. The fragmentation patterns are discussed in terms of the stability of the molecular ions. Comparison with stability values for other organic molecular ions shows that the phthalocyanine molecular ions are amongst the most resistant to dissociation by electron impact. Introduction of a transition metal atom into the phthalocyanine ring system has little effect upon the gaseous ionisation potentials of the complexes. Comparison with extended Hückel calculations suggests that electron impact results in the removal of an electron from either the a_1u(π) or e_u(Np_σ) orbitals of the phthalocyanine ring system. The average difference between the gaseous ionisation potentials and the most probable surface ionisation potentials for the phthalocyanine molecules of 2.34 eV suggest that the polarisation energies for these molecules are much greater than those observed for fused ring aromatic compounds.