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Vibrational Spectroscopies: Quantum Aspects

In certain conditions, accounting for the quantum nature of nuclear motion becomes essential for describing the phenomena under study. For example, when the systems exhibit large amplitude motions or multiple accessible minima, it may be necessary to consider tunneling effects using quantum methods developed by the group [ElVibRot, Tnum-Tana]. In this context, the systems studied include isolated molecules or aggregates [Afansounoudji2023] or those weakly coupled with an environment:

  • Study of molecular hydrogen encapsulated in water clathrates [Lauvergnat2020, Chen2022]: The H2 molecule, trapped in a cage, undergoes fully quantized movements. The spectra associated with the translation, rotation, and vibration of the molecular hydrogen were examined. In the latest study [Chen2022], the coupling between H2 and the first layer of water molecules in the cage was explicitly accounted for (with 125 modes treated quantum mechanically).

Quantum simulation of the H2@clathrate hydrate was performed using a Smolyak algorithm adapted to a system-bath separation method. This approach takes into account the full dynamics of the water molecules in the inner layer while treating the H2O molecules in the second layer as rigid.

  • Study of the tunneling splitting of isolated malonaldehyde [Lauvergnat2023]: In collaboration with André Nauts, this study represents the culmination of several years of methodological developments concerning coordinates and their uses, as well as approaches based on "sparse grids."
  • Study of the hydrated proton [Schröder2022]: The infrared spectrum of the eigen cation, H3O+(H2O)3, was analyzed using quantum simulations performed with MCTDH. In this study, the derivation of the kinetic energy operator (using the Tnum-Tana code) associated with a suitable set of internal coordinates was crucial for the simulations.

Collaborations

Yohann Scribano (LUPM, U. Montpellier), André Nauts (NAPS, U. of Louvain-la-Neuve, Belgium), Zlatko Bačić (New York U., USA), Fabien Gatti (ISMO, U. Paris-Saclay), Oriol Vendrell and Hans-Dieter Meyer (U. Heidelberg, Germany), Komi Sodoga (U. of Lomé, Togo).