Molecular fragmentation and formation processes in PDMS are studied by
measuring and discussing positive and negative ion spectra of pure carbon or
hydrocarbon compounds. Calculations of the hydrodynamic adiabatic expansion of
the material from the inner track result in the formation of carbon clusters in
agreement with the negative ion  spectra. A universal pattern in the negative
ion spectra can thus be explained. Results of molecular breakup  calculations
are compared with the observed positive ions which are assumed to be from the
ultratrack. From the comparision we conclude that the breakup of the carbon
bonds is entropic and takes place during the desorption while the main part of
the hydrogen separation occurs afterwards.