SECONDARY-ION EMISSION FROM FROZEN ALKANES AND BENZENE INDUCED BY MEV-ION IMPACT

Frozen samples of twelve alkanes and benzene were irradiated by Cf-252 fission fragments in order to study secondary ion emission by means o f time-of-flight mass spectroscopy. The mass spectra are to a certain extent similar to electron-impact spectra of gaseous samples. The patt ern of the negative ions could be assigned to dissociation after elect ron capture and frequent collisional reactions in the destruction zone of the nuclear track. Due to the substructure of the mass spectra we emphasize that the bonding type of the negative hydrocarbon ions is mo stly acetylenic. The positive ion spectra strongly depend on the struc ture of the original molecules. They exhibit - contrary to the negativ e ion spectra - molecular ions, cluster ions and molecule-specific fra gment ions. Model calculations were used to investigate the possible s ynthesis of carbon clusters inside an expanding plasma from the infrat rack. For the ultratrack earlier molecular fragmentation calculations are supplemented by modelling the dehydration which is best fitted if assumed to take place subsequent to the fragmentation on a thermal tim e scale. The molecular cluster distributions are calculated by an expl osive breackup model of sputtered material.