Simulating interstellar icy grains in the laboratory

Project highlights:

• This project addresses fundamental questions about the origins of molecular complexity in space, focusing on how the physical and chemical properties of icy dust grains influence the chemistry of interstellar ices in star-forming regions.
• Key outcomes: development of more realistic laboratory analogues of interstellar icy grain mantles; high-resolution infrared spectra that provide new insights into the influence of ice composition and morphology, with direct applications to interpreting observational infrared absorption spectra from James Webb Space Telescope (JWST).
• Training in the use and development of cutting-edge laboratory techniques, including Fourier-transform infrared (FTIR) spectroscopy, vacuum ultraviolet (VUV) spectroscopy, vacuum and cryogenic technology and acoustic levitation, offering valuable skills in both laboratory and analytical research.
• This cross-disciplinary project provides opportunity for engagement with atmospheric physicists, molecular physicists, and astronomers involved in the JWST data analysis, facilitating a direct link between laboratory experiments and space observations.

Dense molecular clouds are the birthplaces of stars and planetary systems. Within these frigid (<10 K), dense regions, ice-coated dust grains serve as microscopic laboratories, driving rich surface chemistry, facilitating gas-grain interactions, and ultimately becoming incorporated into nascent planetary systems. The composition and morphology of these icy grain mantles are determined by the initial conditions within dense clouds. Composed of simple molecular solids (H2O, NH3, CH4, CO2, CO and CH3OH), they subsequently undergo thermal and non-thermal processing (via photon, ion and electron interactions) during cloud collapse and protoplanetary disc formation. These processes drive the formation of complex organic molecules (COMs), enriching the protostellar environments1 . Understanding this chemical evolution is fundamental to unravelling the origin of molecular complexity with profound implications for the molecular origins of life.

Recent high resolution infrared absorption spectra from James Webb Space Telescope (JWST) are providing exciting new details about the properties of interstellar ices along lines of sight towards protostars2 . However, interpreting these spectra and linking them to chemical processes in interstellar environments require comprehensive laboratory spectra measured under controlled conditions that accurately simulate interstellar environments. Astrochemical models also depend heavily on empirical input from laboratory studies, yet many parameters are still extrapolated from a limited dataset. Crucially, most current laboratory spectra are measured through ice films grown on flat cm-sized substrates that are unrepresentative of microscopic 3D ‘fluffy’ interstellar ice grains.

Project description:

This project will exploit fundamental and novel molecular physics laboratory techniques, to investigate the physical and chemical properties of interstellar ice analogues across macroscopic and microscopic scales, in (a) vapour deposited molecular films and (b) acoustically levitated icy aerosols. The macroscopic and microscopic samples offer distinct advantages and challenges as analogues for interstellar ice grains, particularly in terms of thermal properties and the suitability for different experimental approaches. The successful candidate will be involved in designing and conducting a comprehensive comparative spectroscopic study of interstellar ice analogues. (a) Vapour deposited molecular films: Using in situ infrared spectroscopy (Molecular Astrophysics Lab, OU) and vacuum ultraviolet spectroscopy (ASTRID2 synchrotron facility, University of Aarhus, Denmark) this part of the project will focus on ‘traditional’ vapour deposited thin film interstellar ice analogues to probe the vibrational and electronic states of pristine and processed molecular ices3 . Experiments will simulate interstellar conditions, investigating how thermal and non-thermal (e.g. UV) processing drives structural and chemical transformations in condensed films. (b) Acoustically levitated icy aerosols: Scattering effects, which can significantly distort the spectral profiles of interstellar molecular ice bands, are highly dependent on grain size and aggregation4 . In this part of the project icy aerosol particles will be trapped in in the antinodes of an ultrasonic standing wave (acoustic trap) to study their optical properties using in situ infrared and ultraviolet spectroscopy5 . Experiments will explore the effects of particle size, number density distribution in the trap, and thermal and non-thermal (UV) processing. By comparing spectra of levitated particles with those of thin films in (a), the study aims to disentangle the changes observed in the spectra due to ice composition and morphology from the optical scattering effects (Mie scattering in the infrared and Rayleigh scattering in the ultraviolet). The combined VUV and IR study will offer a comprehensive understanding of the physical and chemical properties of the ice analogues, and the laboratory IR absorption spectra will be used for direct comparison and interpretation of observational JWST ice absorption spectra in various protostellar environments.

We seek an enthusiastic and highly motivated candidate with an interest in molecular physics, physical chemistry or astrochemistry and a willingness to learn, develop and integrate a variety of laboratory techniques to acquire and analyse high quality systematic laboratory data. The successful candidate will work in a stimulating and nurturing laboratory research environment within the School of Physical Sciences and be involved in planning and writing proposals for competitive beam time and participating in experimental runs at international facilities. The interdisciplinary laboratory project will provide opportunity to collaborate with other OU research groups including astronomers (with access to JWST ice data), theoretical and experimental physicists and chemists, planetary scientists (investigating cometary and planetary ices), as well as participate in knowledge exchange between laboratory astrochemistry, atmospheric physics, molecular clusters and aerosol communities.

Qualifications required: Ideally a 4-year integrated Masters level qualification in Physics, Astronomy or Chemistry.