Infrared spectroscopy of α-pinene ices irradiated by energetic ions at temperatures relevant to astronomical environments

Abstract

The effects of cosmic-ray bombardment of chiral molecules in the interstellar medium are simulated in the laboratory by performing radiolysis experiments of pure $\alpha$-pinene ices at four different temperatures. The identification and significance of $\alpha$-pinene have not been fully understood because of the insufficient amount of spectral information of these compounds at low temperatures. A comparison of the temperature dependence of the mid-infrared spectra of pure $\alpha$-pinene ices before and after irradiation its irradiation by 61.3 MeV ⁸⁴Kr${}^{15+}$ ions is performed. Mid-infrared Fourier transform (FTIR) spectroscopy was used to follow the changes in the chemicals, which allowed us to characterize the reaction products. This is the first time that the temperature dependence of $\alpha$-pinene’s radiolysis is determined; measurements occurred at 10, 50, 100 and 130 K. The spectra of non-irradiated samples are compared with those of samples irradiated by heavy ions. The new complex organic molecules (COMs) formed by radiolysis at different temperatures are non-chiral and contain up to six carbon atoms (e.g. benzene).