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MO: Fachverband Molekülphysik

MO 3: Theory: Quantum Chemistry and Molecular Dynamics

MO 3.7: Vortrag

Montag, 8. März 2010, 18:15–18:30, F 102

Quantum-induced symmetry breaking explains infrared spectra of CH₅⁺ isotopologues — •Sergei Ivanov, Alexander Witt, and Dominik Marx — Lehrstuhl für Theoretische Chemie, Ruhr–Universität Bochum, 44780 Bochum, Germany

Protonated methane, CH₅⁺, has been investigated intensively using a host of different experimental and theoretical techniques since decades, see Ref. [1] for a review. This is due to the correlated large amplitude motion of its five protons around the carbon nucleus that leads to so–called hydrogen scrambling and causes a fluxional molecular structure. Although the protons and deuterons can easily visit all five sites due to vivid scrambling motion, the occupation of the topologically different sites is found to be strongly non–combinatorial and thus non–classical. This is a purely quantum–statistical effect implying a breaking of the classical symmetry of the site occupations induced by zero–point fluctuations, which are governed by the different masses of H and D [2]. Importantly, this quantum-unduced symmetry breaking is the key for understanding of the spectral changes occurring upon gradual deuteration of CH₅⁺. Ab initio MD in combinations with techniques based on Feynman’s formulation ofquantum statistical mechanics in terms of path integrals allow us to fully reproduce the experimental spectra. Moreover, an in–house developed analysis technique enables full assignment of spectral features to molecular motions.

[1] P. Kumar P. and D. Marx, Phys. Chem. Chem. Phys. 8, 573 (2006)

[2] D. Marx and M. Parrinello, Nature 375, 216 (1995)