A PLASMA DESORPTION MASS-SPECTROMETRY OF CHN+ AND C2HN+ ION FORMATION FROM FROZEN ORGANIC-SURFACES

Cyclohexane, cyclohexene, 1,3-cyclohexadiene and benzene frozen targets have been bombarded with Cf-252 fission fragments and the desorbed ions have been analyzed by time-of-flight mass spectrometry. The behavior of the desorption yields of the CHn+ ions (mass 12-16 u) and C2Hn+ ion (mass 24-30 u) has been studied as a function of both the target stoichiometry and the fragment molecular structure. Because these results show strong evidence of atomization followed by a recombination process inside the fission fragment track, a quasi-equilibrium plasma model is proposed for the desorption mechanism of these species. Moreover, assuming a local thermodynamic equilibrium, the abundance of neutral and ionic species was determined. It is shown that, for appropriate conditions of temperature and pressure inside the track, these calculations reproduce qualitatively the plasma desorption mass spectra of the above C-6 cyclohydrocarbons in the 12-30 u mass range.