Irradiation of Phenylalanine at 300 K by MeV Ions

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 the subject of investigation. This work aims at studying, in the laboratory, the Phe radiolysis by cosmic analogues. The Phe destruction rate, at 300 K, is measured for H, He, and N ion beam irradiation in the 0.5 to 2 kinetic MeV range. Fourier transform infrared (FTIR) spectroscopy was employed to monitor the molecular degradation as a function of fluence. The Phe apparent destruction cross-section, σ^ap, which includes radiolysis and sputtering processes, is determined to be proportional to the electronic stopping power, S. The measured parameter D₀ = 14.3 ± 2.2 eV/molec in the relationship, and $$ = S/D₀ is interpreted as the mean absorbed dose necessary to dissociate or eject a Phe molecule. The Phe half-life in the interstellar medium is predicted to be about 10 million years, H⁺ ions the main destructive cosmic ray constituent.