Physicochemical Properties of α-Pinene in Water Ice Analogs under Energetic Heavy-Ion Irradiation

Abstract

Studying the physicochemical properties of ice in astronomical environments is crucial to understanding the chemical processes involved in cosmic events such as comet and planet formation. The physical characteristics and chemical evolution on the surfaces of cosmic objects such as comets or interstellar grains offer key insights into these processes. This study focuses on α-pinene, a carbon- and hydrogen-rich molecule, which serves as a model for investigating radical-driven synthesis of more complex molecules under space-like conditions. It also provides a useful analogy for complex terrestrial organic molecules and sheds light on how organic matter interacts with water and radiation in extraterrestrial environments. In this work, we simulate the effects of heavy-ion cosmic ray bombardment on chiral molecules in the interstellar medium by analyzing the radiolysis of a C10H16/H2O (1:1) mixture irradiated with 61.3 MeV84Kr15+ions. Fourier Transform Infrared (FTIR) spectroscopy is employed to monitor the chemical evolution of ice samples at 10 K, both before and after irradiation. We identify 12 CnHmand ten CnHmOkmolecules, including complex products such as naphthalene (C10H8), glycolaldehyde (HCOCH2OH), and methyl formate (HCOOCH3). The most abundant hydrogenated product is acetylene (C2H2), followed by naphthalene (C10H8), while the most abundant oxygenated molecules are vinyl alcohol (CH2CHOH) and ethanol (CH3CH2OH). Notably, the formation of CO2is minimal in this experiment. The destruction cross-sections of α-pinene and water in the (1:1) mixture are determined to be 3.5 and 6.4 × 10–13cm2, respectively. The formation cross-sections for the products resulting from radiolysis are on average 2 × 10–14cm2for hydrocarbons and 0.6 × 10–14cm2for the oxygenated products.