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Laser-induced alignment and imaging of molecules embedded in helium nanodroplets

Date Mo, 26.08.2019 - Mo, 26.08.2019
Time 16:45
Speaker Prof. Henrik Stapelfeldt, Department of Chemistry, Aarhus University, Denmark
Location ETHZ, Hönggerberg Campus, HPF G-6
Program I will show how laser pulses can align molecules in helium nanodroplets and how the ability to place molecules in advantageous spatial orientations allows structural determination of molecular complexes. The talk will focus on the following topics:

1) Alignment of molecules with pulses much shorter than the molecular rotational periods.
The experimental results show rotational dynamics that differs completely from that of isolated molecules [1]. Notably, pronounced oscillations in the time-dependent molecular alignment, with no counterpart in gas phase molecules, are observed. Angulon theory identifies the oscillations to originate from the unique rotational structure of molecules in He droplets and transfer of rotational angular moment to the many-body He environment on picosecond timescales [2].

2) Alignment induced by pulses turned-on (quasi) adiabatically.
It will be shown how the 0.4 K temperature of the molecules inside the droplets enables unprecedented high degrees of alignment, in either one or three dimensions. The method applies to large, complex molecules and the alignment can be made field-free by rapidly switching off the alignment pulse [3].

3) Structure determination of molecular complexes using Coulomb explosion imaging.
Results for both dimers of small linear molecules, including CS2 [4] and OCS [5], and dimers of tetracene molecules [6], are presented. Perspectives for time-resolved imaging of bimolecular reactions and interactions are discussed.

[1] B. Shepperson, A. A. Søndergaard, L. Christiansen, J. Kaczmarczyk, R. E. Zillich, M. Lemeshko, and H. Stapelfeldt, Phys. Rev. Lett. 118, 203203 (2017).
[2] I. N. Cherepanov, G. Bighin, L. Christiansen, A. V. Jørgensen, R. Schmidt, H. Stapelfeldt, and M. Lemeshko,, submitted (2019)
[3] A. S. Chatterley, C. Schouder, L. Christiansen, B. Shepperson, M. H. Rasmussen, Henrik Stapelfeldt, Nat. Comm. 10, 133 (2019).
[4] J. D. Pickering, B. Shepperson, B. A. K. Hubschmann, F. Thorning and H. Stapelfeldt, Phys. Rev. Lett. 120, 1121321 (2018).
[5] J. D. Pickering, B. Shepperson, L. Christiansen and H. Stapelfeldt, J. Chem. Phys.149, 154306 (2018).
[6] C. Schouder, A. S. Chatterley, F. Calvo, L. Christiansen, and H. Stapelfeldt, Struct. Dyn. in press (2019).
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