Ionization of uracil molecule in collisions with 2.5-MeV/u Si12+ ions

Abstract

The energy and angular distribution of electron emission from a RNA base molecule, uracil (C 4 H 4 N 2 O 2), are investigated in collisions with 2.5-MeV/u Si12+ ions under high perturbation strength. The absolute double differential cross sections (DDCS) are measured using electron spectroscopy for emission angles between 20° to 160° in the electron energy range 1-620 eV. The single differential cross sections (SDCS) are evaluated by integrating the DDCS over emission angles or energies. The measured cross sections (DDCS and SDCS) are compared with the state-of-the-art continuum distorted wave-eikonal initial state (CDW-EIS) theoretical model. The DDCS obtained by the CDW-EIS is found to provide better agreement with the measurements in the backward angles. With an increase in perturbation strength from 0.5 to 1.19 a.u., the DDCS is found to increase by 10 times in comparison to the earlier reported uracil data for 3.5-MeV/u bare C-ions [Phys. Rev. A 87, 032716 (2013)]. The significant enhancement in the TCS is found for the total cross section in case of Si12+ ions over that predicted by a scaling law as derived for lower charge state projectiles. The forward-backward angular asymmetry is found to increase monotonically with the velocity of emitted electrons and shows very good agreement with the model. For a comparative study, the DDCS is also measured for oxygen molecule using same ion impact, which is found to be about ten times lower than that for the uracil. The forward-backward angular asymmetry for oxygen is found to be almost the same as uracil.