Ultrafast photoexcitation dynamics of atoms and molecules inside helium nanodroplets
Markus Koch
Institute of Experimental Physics, TU Graz
https://tugraz.webex.com/tugraz/j.php?MTID=mb4a9f2f408c4f62d047f9f781fac0630
11:15 - 12:15 Wednesday 11 May 2022 PH01150 Superfluid Helium nanodroplets (HeN) offer fascinating opportunities for spectroscopic studies of atoms, molecules and aggregates because of their low temperature of 0.4 K and the high degree of control in loading the droplets. Systems investigated with frequency-domain spectroscopy include charge and energy transfer in tailor-made or weakly bound aggregates, and the investigation of solvent influence in a growing microsolvation environment. Here, we present the development of HeN for time-domain studies, aiming at a broad application of these nano-cryo-reactors to investigate the dynamics of photophysical and photochemical processes in real time.
In a first step, we were able to observe the photoexcitation dynamics of a single atom (In) solvated inside a HeN with femtosecond time-resolved photoelectron spectroscopy [1,2]. This experiment yields three important findings: (i) it demonstrates that photoelectrons are a good observable for ultrafast processes inside HeN, (ii) it enabled a characterization of the response of superfluid He to photoexcitation of solvated atoms/molecules and, (iii) it showed that these processes can be modeled with time-dependent helium density functional theory simulations.
In a second step, we investigated the HeN influence on coherent nuclear dynamics, by exciting a vibrational wave packet (WP) in dimer molecules (In2) [3]. Very surprisingly, we find that the coherent WP signal can be observed for tens of picoseconds, demonstrating that the perturbation imposed by this quantum liquid can be lower by a factor of 10-100 compared to any other solvent.
Finally, in a recent effort to characterize the propagation of free electrons within the helium nanodroplets, we were able to demonstrate laser-assisted electron scattering, an energy transfer process of strong laser fields and free electrons, for the first time in the condensed phase [4].
References
[1] Nat. Commun. 9, 4006 (2018)
[2] J. Chem. Phys. 152, 014307 (2020)
[3] Phys. Rev. Lett. 124, 115301 (2020)
[4] Nat. Commun. 12, 4204 (2021)
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Institute of Solid State Physics
