Molecular size effects in fast heavy ion induced desorption of biomolecules

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Abstract
Fast ion induced desorption yields of positive secondary ions of different biomolecules have been studied with a time-of-flight technique. The yields were studied as a function of energy deposition of the primary ion. The samples used were an amino acid, two protected oligonucleotides and a small protein (bovine insulin). Different primary ions with constant velocity were used throughout the experiment. In this way the energy density or electronic stopping power was changed by using different primary ions. It was found that for low energy densities the yields increase with different powers of the energy density for the different systems. For high energy densities the yields are proportional to the energy density for all systems studied. The results indicate that for large molecules multiple bond breaking is needed for desorption to occur. For the amino acid sample (valine) an extensive clustering effect was also found. Cluster ions containing as many as 20 valine molecules were observed. This work was supported by the Swedish Natural Science Research Council.