Non-thermal desorption of complex organic molecules in protoplanetary disks: a computational study Aneesa Ahmad and Catherine Walsh University of Leeds, UK Stars and their surrounding planetary systems form within dense molecular clouds. During the gravitational collapse of these clouds, dust and gas flows through a collapsing envelope, feeding a so-called protoplanetary disk, providing the material required to form a new planetary system. 1 The cold midplane of protoplanetary disks is seeded with ices that originally formed on dust grains at the low densities (10 3 – 10 4 cm -3 ) and temperatures (10 K) in the parent molecular cloud. 2 Infrared observations of molecular clouds have well-characterised the composition of these ices. They are mainly composed of simple hydrogenated species such as H 2 O, CH 4 , and NH 3 , with CO and CO 2 ices also forming when the temperature is low enough for CO to freeze out (<; 20 K). CO-rich ices can subsequently react with atomic hydrogen to form larger and more complex species such as H 2 CO and CH 3 OH, the processing of which via heat and/or radiation can further enhance the chemical complexity of interstellar ices. 4 The presence of complex organic molecules (in the form of gas-phase methanol) in protoplanetary disks have finally been revealed around solar-type stars in observations with ALMA (the Atacama Large Millimeter/ submillimeter Array); 5 the methanol is found to be rotationally cold and likely arising from non-thermal desorption from the cold icy reservoir in the disk midplane. 6 In this work we have carried out theoretical modelling of the non- thermal desorption of complex organic molecules in water-rich ices by stellar UV radiation. Our aims are to predict the desorption outcomes and yields for ices irradiated by a range of radiation fields suitable for young stars and for the different ice environments expected in planet-forming disks. In this poster, we explain the motivation behind this work, and show the results of some preliminary simulations. This research has been carried out using molecular dynamics simulations performed using the GROMACS software package. References 1. Ewine F. van Dishoeck and Edwin A. Bergin. “Astrochemistry associated with planet formation.” arXiv preprint arXiv:2012.01472 (2020) 2. Jes K. Jørgensen, Arnaud Belloche, and Robin T. Garrod. “Astrochemistry during the formation of stars.” Annual Review of Astronomy and Astrophysics 58 (2020): 727-778. 3. Boogert, A. C. A., Gerakines, P. A., and Whittet, D. C. B. “Observations of the Icy Universe.” Annual Review of Astronomy and Astrophysics 53 (2015): 541-581. 4. Öberg, K. I. “Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules.” Chemical Reviews 116 (2016): 9631−9663. 5. Walsh, C., Loomis, R. A., Öberg, K. I., et al. “First detection of gas-phase methanol in a protoplanetary disk.” The Astrophysical Journal Letters 823 (2016): L10 6. Ilee, J. D., Walsh, C., et al. in prep
P02
© The Author(s), 2023
Made with FlippingBook Learn more on our blog