Quantum dynamical modelling of photochemistry in space

Understanding chemistry in the interstellar medium requires, at the fundamental level, a mechanistic understanding of the various processes taking place. Many steps in the large reaction networks involve photochemical reactions and dissociation plays a particularly important role. From a theoretical standpoint, modelling such processes is challenging due to the highly non-equilibrium nature of the problem. In this presentation, it will be demonstrated how accurate quantum chemistry methods can be used to characterise excited states of key complex organic molecules (e.g. methanol, formaldehyde, formic acid), and how quantum dynamical simulations that solve the time-dependent Schrödinger equation are then able to fully describe dissociation pathways accessible in a given range of wavelengths. Quantitative, wavelength-dependent branching ratios can be automatically obtained for each channel, along with their timescales, which offers valuable information for interstellar chemistry models.  Furthermore, a newly developed procedure is also discussed, which allows these same quantum dynamics simulations to be performed in an explicit, atomistic environment. This opens up exciting pathways to fully understand the role of interstellar ices at the atomic and molecular level, and how it affects photochemistry. The overarching goal of this work is to rationalise how chemical complexity builds up in space through the development of high-level theoretical descriptions of key phenomena.