Molecular Synthesis in Astrophysical Ices

The continuous cycle of star formation, evolution and death is driven by a complex interplay between interstellar gas, dust and radiation [1]. The interstellar medium (ISM) is a rich chemical factory, with over 170 molecular species identified to date [2], mostly observed in star-forming regions. Star formation begins in dense molecular clouds, where cold (~10 K) interstellar dust provides the surfaces for atoms and molecules to "freeze-out", forming icy mantles. These icy mantles are the largest molecular reservoirs in the ISM, where chemical reactions, driven by both non-thermal and thermal processes, produce more complex molecules that are subsequently released into the gas phase [3]. At the OU Astrochemistry laboratories, we investigate the physical and chemical properties of astrochemical ices in a controlled laboratory environment using ultra-high vacuum chambers and cryogenically cooled substrates to grow interstellar ice analogues [4-6]. The ices are characterised in situ, using Fourier-Transform Infrared Spectroscopy (FTIR) on-site or Vacuum Ultraviolet spectroscopy via access to synchrotron facilities (ASTRID2 in Aarhus, Denmark; and, in partnership with Dr Bhala Sivaraman at PRL in India, the Taiwan Synchrotron facility). The FTIR and VUV spectra are highly sensitive to the ice morphology and the interaction between the molecular species in the ice, and are also used to monitor any changes as a result of thermal (controlled heating) or non-thermal (UV, electron or ion irradiation) processing. Additionally, mass spectroscopy is used to monitor the species that are released into the gas phase (desorption and sputtering) during processing. Recent advances include the development of more realistic dust grain mimics using nanofabrication techniques to fashion carbonaceous and silicate microstructures to act as a grain template for ice deposition. We are also exploring use of ultrasonic levitation of dust grains as a method for studying astrochemistry on isolated grains.