DEL FRE Samuel: Theoretical studies of photodesorption of molecular interstellar ices.

Summary of the thesis:

The objective of the proposed thesis is to provide a better understanding of the impact of the photochemistry of molecular ices on the physicochemistry of the interstellar medium. It is 100% funded by the ANR PIXyES "Photodesorption Induced by UV-X-rays and Electrons on ice Surfaces". The main objective of this work is to understand, at the mole level, the distribution of electronic excitation energy vibrations following a VV radiation. This redistribution then leads to the deception of a molecule from its pure ice or mixtex. To do this, it is necessary to determine with precision the probability of photodesorption as well as the kinetic energy distributions is rovibrational of the desorbed molecule. Two strategies will be considered. The first one [1] qualified of standards will include three steps. 1)- obtaining the ab initio interaction energies of the CO-CO, N2-N2, N2-CO, and H2O-CO dimers through electronic structure calculations; 2) construction, from these data, of the analytical potential energy surfaces of these dimers. Finally, 3)- the force fields will allow the construction of clusters, then crystalline and amorphous ices which will be used in classical simulations of the photodesorption of these interstellar ices. The second strategy, more innovative [2], will be explored by using jointly the methods of: Ab Initio Molecular Dynamics (AIMD) [3], Surface Hopping [4] and "TIme dependent density functional theory" [5] (TDDFT). The combination of these methods has the advantage of relying on a smaller number of approximations and allows to explore the true potential energy surface now explicitly influenced by the environment. The results of this study will be compared to experiments, on the same systems, performed by two partner teams of this ANR project.

[1] M. C. van Hebert, J. Takahashi, E. F. van Dishoeck, J. Phys. Chem. A 2015, 119, 6354.
[2] A. J. DeSimone, V. D. Crowell, C. D. Sherrill, T. M. Orlando, J. Chem. Phys. 2013, 139, 164702.
[3] E. Tapavicza, G. D. Bellchambers, J. C. Vincent, F. Furche, Phys. Chem. Chem. Phys. 2013, 15, 18336.
[4] J. C. Tully, R. K. Preston, J. Chem. Phys. 1971, 55, 562.
[5] J. M. Liu, Y. Zhai, X.-L. Zhang, H. Li, Phys. Chem. Chem. Phys. 2018, 20, 2036. 

PhD student: DEL FRÉ Samuel - LinkedIn

PhD supervisors: MONNERVILLE Maurice - TOUBIN Céline - RIVERO SANTAMARIA Alejandro