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MO: Fachverband Molekülphysik

MO 17: Theory

MO 17.8: Vortrag

Donnerstag, 12. März 2020, 15:45–16:00, f142

On the Molecular Symmetry of Protonated Methane — •Stefan Brackertz¹, Benjamin Nukic¹, Thomas Salomon¹, Per Jensen², and Stephan Schlemmer¹ — ¹I. Physikalisches Institut, University of Cologne — ²Physikalische und theoretische Chemie, Universität Wuppertal

The energy term diagram of the lowest energy ro-vibrational states of CH₅⁺ has eluded any analytical description until Schmiedt et al. proposed a 5d superrotor model in 2015. In 2018 Fábri and Császár used quantum graphs to describe the internal motions. Numerical results have been published in 2016 by Wang et al. All of these approaches describe the experimental energies resonably well but seem to be incompatible regarding molecular symmetry.

We present results on the relations between these approaches:

• Schmiedt et al. showed the non-existence of equivalent rotations for the permutations of CH₅⁺ because S₅ is not isomorphic to any subgroup of SO(n)×{E,E^*} for n < 5. This can also be understood geometrically using the results of Fábri and Császár.
• Fábri and Császár do a splitting of S₅=S₄×S₂ associated with an internal equivalent rotation for the S₄ part. This approach gives some clues to the interpretation of the 5d superrotor model.

These considerations are also used for the modeling of a simpler case of a fluxional molecule, He−H₃⁺, which is subject to internal as well as end-over-end rotation.