I. Dynamics of complex molecular systems
1) Modelling of processes at interfaces relevant to atmospheric physical chemical chemistry
a. Photodissociation on ice surfaces
Photodynamics of adsorbed molecules on ice is described using Quasi Classical Trajectories and Time Dependent Wave Packets methods including thermal induced surface disorder. (S. Woittequand, D. Duflot, M. Monnerville, B. Pouilly, C. Toubin, S. Briquez, and H.-D. Meyer, The Journal of Chemical Physics 127, 164717 (2007)[DOI: 10.1063/1.2799519] & S. Woittequand, C. Toubin, M. Monnerville, B. Pouilly, S. Briquez, and S. Picaud, Surface Science 601, 3034 (2007)[DOI:10.1016/j.susc.2007.05.006])
b. Organization of model aerosol particles
Palmitic acid coated salt at 30% RH
Classical Molecular Dynamics simulations associated with force-field parametrization, (Gromacs, Polaris (MD)…) are extensively used to characterize the molecular organization within or at the surface of model aerosol particles. (J. Lovrič, D. Duflot, M. Monnerville, C. Toubin, and S. Briquez, J. Phys. Chem. A 120, 10141 (2016) [DOI:10.1021/acs.jpca.6b07792
).
Data extracted from molecular dynamics simulations can also be compared to experimental data. (DOI:10.1039/C8CP04151B) pubs.rsc.org/en/content/articlelanding/2019/cp/c8cp04151b.
Calculated absolute ionization cross section of C60+ ion for different electronic temperatures, obtained with real-time Time-Dependent Density Function Theory (rt-TD-DFT), see https://www.synchrotron-soleil.fr/en/news/soleil -highlights-2017. (S. Douix, D. Duflot, D. Cubaynes, J.-M. Bizau, and A. Giuliani, J. Phys. Chem. Lett. 8, 7 (2017) [DOI : 10.1021/acs.jpclett.6b02558])
a. Reactive collisions
The improvement of astrophysical models of the chemistry of the interstellar medium requires precise kinetic data such as photodissociation cross sections or the rate constants of key elementary reactions. In many cases, for example when several radicals are involved, theoretical calculations are the only way to get these data. The PCMT team develops quasi-classical trajectory (QCT) and time-dependent quantum wave packet (TDWP) codes to study the dynamics of reactive collisions as well as the dynamics of photodissociation processes. For example, we have recently studied, both classically and at the quantum levels, the Si(3P) + OH(X2Π) → SiO(X1Σ+) + H(2S) reaction, which is the main pathway for the formation of interstellar SiO in the gas phase. The SiO molecule is considered by astrophysicists as a tracer of the cold regions of the interstellar medium and thus plays an important role. In addition to the reaction rate constant k(T), for a whole temperature range [10 K - 500 K], many other results such as integral cross sections and rovibrational energy distributions of the SiO product have been obtained. The quantum rate constant is broadly in agreement with the classical ones but differs significantly from the temperature-independent value currently used in astrochemical databases. This difference shows the interest of our theoretical approaches for models of physicochemistry of the interstellar medium.
A. Rivero Santamaría, F. Dayou, J. Rubayo-Soneira, and M. Monnerville, J. Phys. Chem. A 121, 1675 (2017); DOI:10.1021/acs.jpca.7b00174; .
A. Rivero Santamaría, P. Larregaray, L. Bonnet, F. Dayou, and M. Monnerville, J. Phys. Chem. A 123, 7683 (2019); DOI:10.1021/acs.jpca.9b04699;.
b. Adsorption on ice surfaces, spectroscopy and ionization potentials.
Prediction from classical MD and hybrid QM/MM calculations of adsorption energies, diffusion barriers, ionization energies for molecules or radicals on crystalline and amorphous ices. (E. Michoulier, J. A. Noble, A. Simon, J. Mascetti, and C. Toubin, Phys. Chem. Chem. Phys. 20, 8753 (2018) [DOI: 10.1039/C8CP00593A]; E. Michoulier, N. Ben Amor, M. Rapacioli, J. A. Noble, J. Mascetti, C. Toubin, and A. Simon, Phys. Chem. Chem. Phys. 20, 11941 (2018) [DOI:10.1039/C8CP01175C)