Investigation of a Fragmentation Model for n-Paraffins

A fragmentation model is postulated for the interpretation of n-paraffin mass spectra. It is assumed that primary dissociations of molecule ions yield fragment ions containing at least half the total number of available carbon atoms. Any fragment ions retaining sufficient excitation energy can dissociate further, with the same product size limitations as in the primary processes. At each step, all possible dissociations are assumed to be in competition. Rate constants are calculated by the statistical theory. Breakdown curves are given for n-decane, and described for other cases. The model can successfully account for observed patterns, their dependence upon the ionizing voltage, and the occurrence of several metastable ion peaks. However, other expected metastables do not appear, the requisite internal energy distributions cannot presently be reconciled, and the calculated amounts of fragment-ion labeling from C13-enriched molecules are in disagreement with experimental results.