APPLICATION OF A TANDEM ANALYZER TO SIMS STUDIES OF HYDROCARBON POLYMERS

The fragmentation of ions sputtered from the surface or low-density poly(ethylene) (LDPE) has been investigated by studying their collisionally activated dissociation (CAD) when incident upon a variety of target gases in the collision cell of a triple quadrupole SIMS instrument. It was found that heavier targets resulted in more extensive CAD than was observed with lighter targets but that sulphur hexafluoride is an inefficient target because of the amount of energy that is transferred to its vibrational modes of motion (rather than being available to induce fragmentation in the parent ion). The behaviour observed for an oxygen target was quite different to that observed for other targets (at higher pressures). In general, oxygen induced markedly greater fragmentation for the small parent ions, but xenon was the preferred target for the larger parent ions. Fragmentation patterns could readily be assembled for all of the parent ions observed in the SIMS spectrum of LDPE using the CAD data. There are good indications that the data obtained may assist in identification of ion structures and in elucidation of general rules governing the fragmentation of organic materials during SIMS. For example, LDPE fragment ions were found to obey quite strictly the Even Electron Rule, a well-known rule in mass spectrometry.