The search for realistic interstellar ice analogues: ice films, icy aerosols and molecular clusters

Supervision team: Anita Dawes, Sam Eden External supervisor: Nigel Mason

Lead contact: Anita Dawes – [email protected]

Description: Over 200 molecular species have been identified in the interstellar medium (ISM), many of which are complex organic molecules (COMs). Elucidating the formation of COMs in the ISM and their evolution through the star formation process is fundamental to our understanding of the origins of the molecular building blocks of life. It is now widely accepted that many of the COMs observed in the ISM are synthesized within microscopic icy grain mantles and are subsequently released into the gas phase via thermal and radiation-induced processes during star formation. Most of what we know about the physical and chemical properties of these interstellar ices comes from the direct comparison of observational data from infrared telescopes (ISO, Spitzer, AKARI, VLT) with spectroscopic laboratory data. As such, efforts to elucidate the key reactive processes in the formation of COMs are hampered by the difficulty of producing laboratory samples that mimic interstellar ice grains. Most laboratory astrochemistry studies to date have been conducted by growing ices on large (cm-sized) flat substrates that are unrepresentative of interstellar ice grains. This raises key questions in Astrochemistry: (1) are the physical and chemical properties of such macroscopic laboratory ice samples analogous to those of the ices covering microscopic 3D fractal-like particles found in the ISM and (2) how does this affect the formation of COMs?

This project aims to address these questions head-on by making direct comparisons between the ‘traditional’ laboratory astrochemistry experiments on macroscopic ice films with microscopic ice analogues in the form of icy aerosols and molecular clusters. The macroscopic and microscopic samples have contrasting strengths and weaknesses as analogues for interstellar ice grains, notably in terms of thermal properties and the types of experiments applicable. The successful candidate will have the unique opportunity to carry out complementary experiments at two collaborating laboratories within the School of Physical Sciences: The Astrochemistry Laboratory (Dawes) and the Molecular Clusters Laboratory (Eden, http://physics.open.ac.uk/clusters/). The physical and optical properties of macro- and micro-icy grain analogues will be studied by comparing infrared spectroscopic signatures of vapour deposited ice films [1] with acoustically levitated (nm-µm) icy aerosols [2]. Subsequently, radiation-driven processes will be investigated by comparing electron and photon irradiated ice films with equivalent processing of molecular clusters (typically up to 10 molecules) and monitoring the reaction products using a combination of infrared spectroscopy and mass spectroscopy [2]. This data will be valuable for planning and informing observational programmes such as the upcoming launch of James Webb Space Telescope to probe for COMs in star forming regions. Furthermore, the project will provide new insights into the key question in astrochemistry of how best to mimic interstellar icy grains in the laboratory and have a significant impact in the effort to understand the formation of COMs in star forming regions and on the origins of the molecular building blocks of life.

We seek an enthusiastic and highly motivated candidate with an interest in Astrochemistry and a willingness to learn and develop laboratory techniques to acquire high quality laboratory data. The successful candidate will work in a stimulating and nurturing research environment as part of two open and friendly cross-disciplinary laboratory groups.

References: [1] Dawes et al. PCCP 18 (2016) 1245 [2] Mason, (Dawes) et al. Faraday Discuss. 137 (2008) 367-376 [3] Ghafur et al. J. Chem. Phys. 149 (2018) 034301

Qualifications required: A First Class or Upper Second class MSci degree in Physics, Chemistry or related discipline. Previous experience in vacuum technology and experimental techniques such as FTIR and Mass Spectroscopy.