Decoding Cosmic Chemistry: Laboratory Insights into A-Pinene Radiolysis in Space-Like Conditions

A recent study published in Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy explored the relationship between radiation and molecular evolution. Led by A. L. F. de Barros from the Centro Federal de Educação Tecnológica Celso Suckow da Fonseca in Rio de Janeiro, Brazil, the research team studied how the chiral molecules of pure a-pinene ices change at temperatures felt on extraterrestrial environments (1).

A-pinene is a chiral molecule of the monoterpene class, and it has been found in many plants, such as conifers (2). A-pinene has played a key role in the fragrance industry, and it is often found in terrestrial plant-derived products (1,2). A-pinene, therefore, is thought to have many therapeutic properties (3).

Recently, a-pinene has fascinated researchers for its structural complexity and as a precursor to other compounds. In particular, scientists believe that a-pinene and its behavior under cosmic conditions could help explain how cosmic rays interact with molecules in the interstellar medium (1).

As a result, the researchers in this study attempted to fill a void by investigating this topic, where little research exists. In their study, the researchers simulated cosmic-ray interactions in a controlled laboratory setting (1). Then, the researchers tracked chemical composition changes in a-pinene after exposing it to 61.3 MeV ⁸⁴Kr¹⁵⁺ heavy ions using mid-infrared (IR) Fourier transform (FT-IR) spectroscopy (1). As part of the experimental setup, the researchers cooled a-pinene ices at four temperatures, which were 10, 50, 100, and 130 K. By expanding the temperature range, the researchers sought to gain a better understanding of the temperature-dependent radiolysis of a-pinene.

The researchers observed distinct changes in the IR spectra of a-pinene ices before and after irradiation, revealing the formation of new complex organic molecules (COMs) (1). These radiolysis products, which include non-chiral compounds containing up to six carbon atoms (such as benzene), provide clues about chemical pathways relevant to the formation of prebiotic molecules in space (1).

Radiolysis experiments and their outcomes are often determined by temperature (4). While the temperature range can vary based on the type of experiment being conducted, they often start at a low temperature and gradually increase to assess how the chemical compositions change with the temperature (4). In this study, as temperatures increased, the researchers noted variations in mid-IR band positions, widths, and strengths. The conclusion was that it indicated that molecular reactivity and product distribution are strongly temperature dependent (1). By extending their analysis to 50, 100, and 130 K, the researchers enhanced the applicability of their findings to planetary environments, including icy moons and comets where such conditions prevail (1).

The study's insights are particularly relevant to understanding the chemical evolution of organic molecules in planetary systems. The identification of non-chiral COMs as radiolysis products sheds light on how simple molecules in the interstellar medium might transform into more complex structures under the influence of cosmic radiation (1).

This study also demonstrates the utility of FT-IR spectroscopy. The researchers demonstrated in their study that FT-IR spectroscopy can be used as a tool for probing molecular changes under simulated space conditions (1). The temperature-dependent data generated by this study serve as a valuable reference for interpreting observational spectra of interstellar and planetary ices, potentially aiding future missions to icy bodies in the solar system (1).

By simulating the effects of cosmic rays on a-pinene, this research exemplifies the growing field of laboratory astrophysics, where terrestrial experiments illuminate phenomena occurring in the vast reaches of space (1). The findings not only enhance our understanding of interstellar chemistry, but they also inspire further exploration of how cosmic conditions influence molecular evolution.

References

1. De Barros, A. L. F.; Ricca, A.; da Silveira, E. F. Infrared Spectroscopy of a-Pinene Ices Irradiated by Energetic Ions at Temperatures Relevant to Astronomical Environments. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2025, 329, 125504. DOI: 10.1016/j.saa.2024.125504
2. Allenspach, M.; Steuer, C. a-Pinene: A Never-Ending Story. Phytochemistry 2021, 190, 112857. DOI: 10.1016/j.phytochem.2021.112857
3. Salehi, B.; Upadhyay, S.; Orhan, I. E.; et al. Therapeutic Potential of a- and B-Pinene: A Miracle Gift of Nature. Biomolecules 2019, 9 (11), 738. DOI: 10.3390/biom9110738
4. Herve du Penhoat, M.-A.; Goulet, T.; Frongillo, Y.; et al. Radiolysis of Liquid Water at Temperatures up to 300 ^oC: A Monte Carlo Simulation Study. J. Phys. Chem. A 2000, 104 (50), 11757–11770. DOI: 10.1021/jp001662d