Irradiation of phenylalanine at 300 K by MeV ions

Abstract

Phenylalanine (Phe) is an amino acid that has been identified in carbonaceous meteorites; its formation mechanism in space is unknown, and its radioresistance has been object of investigation. This work aims to study, in laboratory, the Phe radiolysis by cosmic analogs. The Phe destruction rate, at 300 K, is measured for H, He and N ion beam irradiations in the 0.5 to 2 kinetic MeV range. Infrared spectroscopy (FTIR) was employed to monitor the molecular degradation as a function of fluence. The Phe apparent destruction cross‒section, σapd, which includes radiolysis and sputtering processes, is determined to be proportional to the electronic stopping power, Se. The measured parameter D0 = 14.3 ± 2.2 eV/molec in the relationship σapd = Se/D0 is interpreted as the mean absorbed dose necessary to dissociate or eject a Phe molecule. The Phe half-live in the ISM is predicted to be about 10 million years, H+ ions being the main destructive cosmic ray constituent.