Evidence for the formation of dynamically created pre-formed ions at the interface of isotopically enriched thin films.

A novel approach to elucidate the ionization mechanism for the [M + H] molecular ion of organic molecules is investigated by molecular depth profiling of isotopically enriched thin films. Using a model bi-layer film of phenylalanine (PHE) and PHE-D, the results show formation of an [M + D] molecular ion for the non-enriched PHE molecule attributed to rearrangements of chemical damage due to successive primary ion impacts. The [M + D] ion is observed at the interface for 19.9nm in the enriched-on-top system and 9.9nm for the enriched-on-bottom system. This ion formation is direct evidence for dynamically created pre-formed ions as a result of chemical damage rearrangement induced by previous primary ion bombardment events.