You are here: Home Events Seminar Series 2019 … 17.12.19 - Markus Koch "Femtosecond …

17.12.19 - Markus Koch "Femtosecond Photoexcitation Dynamics of Atoms and Molecules inside Helium Nanodroplets"

Institute of Experimental Physics, Graz University of Technology, Graz, Austria
When Dec 17, 2019
from 01:00 PM to 02:00 PM
Where HS II, Physical High Rise
Contact Name
Contact Phone 203 97666
Add event to calendar vCal
iCal

 

 

 

 

 

 

 

 

 

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.

 

 Abstract Markus Koch

 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