Molecular alteration and carbonization of aspartic acid upon N+ ion irradiation

Structural changes of aspartic acid (Asp) irradiated by nitrogen ions of 30 keV were studied using Fourier transform infrared (FTIR) spectroscopy. Significant decreases of the intensities of COO-, NH3+, COOH and CH2 vibrations in the FTIR spectra, compared with those of unirradiated Asp, were observed for the sample irradiated at the fluence of 1 x 10(16) ions/cm(2). The decrease rates of the intensities of COO-, NH3+, COOH and CH2 vibrations with respect to the increasing irradiation fluences up to 4 x 10(16) ions/cm(2) were different. The results were attributable to the nonstoichiometrical desorption of corresponding volatile species such as H-2 NH3+ and CO2. The radiolysis residue of Asp after irradiation at a high fluence of 1 x 10(17) ions/cm(2) was analyzed and fatty acid was detected. (C) 2000 Elsevier Science B.V. All rights reserved.