Elementary processes during collisions of ions with tryptophan molecules

The relative cross sections of elementary processes occurring in single collisions of tryptophan molecules in the gaseous phase with He$^{2+}$ ions with energy 4 keV/u are measured using time-of-flight mass spectrometry for studying the mechanism of radiation damage of amino acid molecules. The fragmentation channels for intermediate singly and doubly charged tryptophan molecular ions formed during one-electron capture, two-electron capture, and electron capture with ionization are investigated. Significant difference is observed in the mass spectra of fragmentation of intermediate doubly charged ions formed during the capture with ionization and double capture, which is associated with different energies of excitation of $\{$C$_{11}$H$_{12}$N$_{2}$O$_{2}\}^{2+}$ ions.