Mechanism of metal cationization in organic SIMS

A mechanism for metal cationization of phenyl group containing hydrocarbons is discussed. Intact molecules and their fragments are emitted from a thin organic layer covering a metal surface bombarded by fast ions. It is shown that the process of associative ionization of a neutral hydrocarbon molecule and a neutral excited metal atom, occurring above the surface, may contribute to the yield of cationized molecules. To demonstrate this we have calculated the potential energy curves for the model system C6H6+Me (Me=Ag, Cu, Au) making use of the density functional theory. The initial states of the metal atoms approaching the benzene ring along the C6 symmetry axis were set as the ground, ionic, and excited in (n−1)d9ns2 electronic configuration.