Astrochemistry concerns the behavior of atoms and molecules in astrophysical environments, which can include star-forming clouds and cores, and circumstellar and interstellar regions. The varied gas-phase chemical compositions of these environments are revealed by radio-telescope observations of molecular spectral-line emission and absorption, primarily in the mm and sub-mm bands. Infrared observations also indicate significant solid-phase abundances of simple hydrides, in the form of ices, which coat the sub-micron sized dust grains that permeate interstellar space. The process of star formation – which involves the heating and UV radiative processing of gas and solid-phase material alike – further encourages the production of complex organic molecules that may contribute to the store of pre-biotic material ultimately available on the surfaces of new planetary bodies.
The Garrod group develops and applies new computational techniques to the study of chemical kinetics in interstellar and star-forming environments. A particular focus of the group is the formation and processing of simple and complex organic molecules on dust-grain surfaces and within astrophysical molecular ices.
New techniques recently developed by the group include a unique, fully three-dimensional, off-lattice kinetic Monte Carlo code that can simulate surface chemistry on dust grains of arbitrary size and shape, over interstellar timescales. The method uses local surface interaction potentials to guide the chemical kinetics and the resultant structure of the ice that forms on the dust-grain surface. The simulated cross-sectional images of interstellar dust-grain ice mantles (below) demonstrate the dependence of ice porosity on physical conditions such as gas density.
Another major focus is the production of complex organic molecules during the star-formation process. The group has developed coupled gas-grain kinetics models to explain recent new detections of organic molecules and to predict interstellar abundances of biologically-significant species, including the amino acid, glycine. The group has also developed dedicated spectral-simulation codes to translate the model results into spectral emission maps, for comparison with observed star-forming cores. The simulated spectra below show predictions for the spectral emission of glycine in a nearby star-forming core.
“Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide.” Belloche, A., Garrod, R. T., Müller, H. S. P. & Menten, K. M., 2014, Science, 345, 1584.
“Three-dimensional off-lattice Monte Carlo kinetics simulations of interstellar grain chemistry and ice structure.”
Garrod, R. T., 2013, ApJ, 778, 158.
“Simulations of hot-core chemistry.” Garrod, R. T. & Widicus Weaver, S. L., 2013, Chemical Reviews, vol. 113, pp. 8939 – 8960.
“A three-phase model of hot cores: the formation of glycine.” Garrod, R. T., 2013, ApJ, 765, 60.
“On the formation of CO2 and other interstellar ices.” Garrod, R. T. & Pauly, T. A., 2011, ApJ, 735, 15.