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Big quantum effects in small molecules

Speaker: Prof. Jörn Manz
Professor, Theoretical Chemistry at Freie Universität Berlin, German
Time: 2018-04-18 10:00
Place: Exhibition Hall, Hefei National Laboratory Building


  We discover surprising consequences of the well-known quantum effects such as zero-point energies, superposition and interferences of quantum states, tunneling, and constraints imposed by nuclear spins. The examples include a new type of chemical bonding: "vibrational bonding" stabilizes BrMuBr at its low, broad transition state due to the reduction of vibrational zero point energies ( Muonium Mu is the light isotope of hydrogen, mMu = mH/9).1a) The large mass ratio enables another effect in molecules, such as FHF, CdH2 or OsH4: well designed circularly polarized laser pulses excite superpositions of degenerate bending or stretching states with strong ring currents of the highly charged nuclei that induce very strong intra-molecular magnetic fields (>600T).1b) By analogy, one can prepare molecules such as Mg-porphyrine in interfering ground and degenerate excited electronic states with strong electronic fluxes ( about 1 e/fs).1c) Analogous preparation of interfering electronic states in molecular ions such as H2+ or HCCI+ yield electronic fluxes that support periodic charge migration from one molecular end to the other, on time scale of few hundred attosecond.2 Laser control of multidirectional charge migration is simulated for C6H6.3 The laser pulse breaks electronic structure symmetry, and that can be restored by a second pulse, the time-reversed copy of the first one, with few attosecond precision of the time delay, also confirmed experimentally for the Rb atom. Likewise, interfering nuclear ground and excited states yield circular and linear tunneling; e.g. in the model B2Cl2F2 and NH3 molecules. Here, analogous time evolutions of the nuclear densities correlate with entirely different tunneling fluxes.4 Electrons may flow with the nuclei, or in oblique directions (e.g. rhomb-to-rhomb isomerization of B4);5a) transient antagonistic electronic fluxes cause electronic restructuring at transition states (e.g. Na2 in excited state with double well potential).5b) Antagonistic nuclear fluxes in vibrating Na2 give rise to the "quantum accordion effect". Finally, the nuclear spin statistics theorem implies surprising quantum effects in systems such as the planar boron rotors, B11, B13+, etc.6 For example, one may calculate their global minimum structures (GM), but it is impossible to prepare them in GM.
1 a)D.G. Fleming, J. Manz, K. Sato, T. Takayanagi, Angew. Chem. Int. Ed. 53, 13706 (2014); b)I. Barth, C. Bressler, S. Koseki, J. Manz, Chem. Asian J. 7, 1261 (2012); c)I. Barth, J. Manz, Angew. Chem. Int. Ed. 45, 2962 (2006).
2 D. J. Diestler, G. Hermann, J. Manz, J. Phys. Chem. A 121, 5332 (2017); H. Ding, D. Jia, J. Manz, Y. Yang, Molec. Phys. 115, 1813 (2017).
3 D. Jia, J. Manz, B. Paulus, V. Pohl, J. C. Tremblay, Y. Yang, Chem. Phys. 482, 147 (2017).
4 T. Grohmann, J. Manz, A. Schild, Molec. Phys. 111, 2251 (2013).
5 a)T. Bredtmann, D. J. Diestler, S.D. Li, J. Manz, J.F. Perez-Torres, W.J Tian, Y.-B. Wu, Y. Yang, H.-J. Zhai, Phys. Chem. Chem. Phys.17,29421 (2015) (Perspective); b)D. Jia, J. Manz, Y. Yang, J. Chem. Phys.148, 041101 (2018) (Comunication).
6 J. Manz, J. F. Perez-Torres, Y. Yang, Phys. Rev. Lett. 111, 153004 (2013); Y. Yang, D. Jia, Y.J. Wang, H.J. Zhai, Y. Man, S.-D. Li, Nanoscale 9, 1443 (2017).

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