17.12.19 - Markus Koch "Femtosecond Photoexcitation Dynamics of Atoms and Molecules inside Helium Nanodroplets"
| When |
Dec 17, 2019
from 01:00 PM to 02:00 PM |
|---|---|
| Where | HS II, Physical High Rise |
| Contact Name | Simone Ortolf |
| Contact Phone | 203 97666 |
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Femtosecond Photoexcitation Dynamics of Atoms and Molecules inside Helium Nanodroplets
Superfluid helium nanodroplets (HeN) represent a promising approach to study femtosecond dynamics in previously inaccessible systems. Here, the first time-resolved investigations of single indium (In) atoms and In2 molecules located inside HeN are presented, which were obtained by combining time-resolved photoelectron and photo-ion spectroscopy and time-dependent helium density functional theory modelling.
In the case of In atoms, photoexcitation triggers an expansion of the He bubble within 600 fs, which is represented by a 300 meV shift of the photoelectron kinetic energy (Fig. 1a) [1]. Simulations reveal that In excited-state electronic energy is converted into He kinetic energy (pressure waves) during this process. The bubble expansion is followed by an oscillation of the He bubble with a period of (28±1) ps, and ultimately leads to ejection of the dopant from the droplet after ~60 ps.
In the case of In2, photoexcitation initiates a very similar response of the He solvent (Fig. 1b) [2]. Superimposed we find a strong periodic modulation of the photoelectron signal, indicating coherent nuclear wave packet (WP) motion of In2 with a 0.42 ps period. The slowly decaying periodic signal reappears after 150 and 300 ps, representing the half and full revivals of the WP, respectively. Appearance of these revivals demonstrates that the He-induced influence on coherent nuclear motions can be lower by a factor of 10-100 compared to conventional solvents.
Fig. 1: Transient photoelectron kinetic energy for In (a) and In2 (b) inside HeN.
References
[1] B. Thaler, S. Ranftl, P. Heim, S. Cesnik, L. Treiber, R. Meyer, A. W. Hauser, W. E. Ernst, M. Koch, Femtosecond photoexcitation dynamics inside a quantum solvent, Nat Commun 9, 4006 (2018)
[2] B. Thaler, M. Meyer, P. Heim, M. Koch, Long lived nuclear coherences inside helium nanodroplets, arXiv:1907.04157, in review
