Quantum dynamics of molecules coupled to helium nanodroplets

• Antragsteller: Professor Dr. Marcel Mudrich; Professor Dr. Walter Strunz
• Fachliche Zuordnung: Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
• Förderung: Förderung von 2011 bis 2017
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 203749362

• Erstellungsjahr: 2017

Zusammenfassung der Projektergebnisse

In this project we carried out a series of experiments to probe the dynamics of photoexcited molecules attached to the surface or embedded inside He nanodroplets. These findings were supported by quantum dynamical calculations based on dissipative quantum dynamics. Previous measurements done with a high-repetition laser had indicated long-lived vibrational and electronic coherences of laser-excited alkali metal atoms and molecules initially attached to the surface of He nanodroplets. ln contrast, when using a laser system with kHz repetition rate thereby excluding the interaction with multiple pulse pairs, no coherent wave packet dynamics was found, neither for alkali molecules at the surface nor for Lil and I2 embedded inside the droplets. We interpret this finding by the efficient dephasing and relaxation of vibrational excitation induced by the He droplet environment. Nevertheless various interesting He droplet-induced dynamics were studied, including vibrational relaxation of RbHe, desorption and ion fall-back of Rb2, complex formation of [IHen]+ and [IHen]-. Moreover, we performed detailed measurements of the complex predissociation dynamics of Lil and I2 in the gas-phase. In both cases, ion-pair states were found to play a crucial role in the dynamics. For the theory part, the most challenging aspect of the project was trying to figure out a path how to determine microscopically the dissipative influence of the He droplet as an "environment" for the quantum dynamics of atoms and molecules. A crucial step towards this goal was finally made: an efficient time-dependent method to determine the underlying bath correlation function was found, based on a suitable auto-correlation function. This bath correlation function can now be used as an input for master or stochastic Schrödinger equations to describe the dissipative and decohering influence of Bose (superfluid) environments. Moreover, as in Fermi's golden rule, in the weak coupling limit an explicit expression for the damping and decoherence rates can be obtained.

Projektbezogene Publikationen (Auswahl)

• "Vibrational relaxation and dephasing of Rb2 attached to helium nanodroplets", Phys. Chem. Chem. Phys. 13, 6816 (2011)
  B. Grüner, M. Schlesinger, Ph. Heister, W. T. Strunz F. Stienkemeier, and M. Mudrich
  
• "Detailed model study of dissipative quantum dynamics of K2 attached to helium nanodroplets", New Journal of Physics 14, 013029 (2012)
  M. Schlesinger and W.T. Strunz
  
• "Formation and relaxation of RbHe exciplexes on He nanodroplets studied by femtosecond pump and picosecond probe spectroscopy', Journal of Chemical Physics 137, 244307 (2012)
  C. Giese, T. Mullins, B. Grüner, M. Weidemüller, F. Stienkemeier, and M. Mudrich
  
• "Photoionization of Pure and Doped Helium Nanodroplets", International Reviews in Physical Chemistry 33, 301 (2014)
  M. Mudrich and F. Stienkemeier
  
• "Predissociation of high-lying Rydberg states of molecular iodine via ion-pair states", Journal of Chemical Physics 140, 124311 (2014)
  Bogomolov A S, Grüner B, Kochubei S A, Mudrich M, Baklanov A V
  
• "Phase-modulated electronic wave-packet interferometry reveals high resolution vibronic spectra of free Rb Atoms and Rb*He molecules", Physical Chemistry Chemical Physics 17, 23877 (2015)
  L. Bruder, M. Mudrich, F. Stienkemeier
  
• "Predissociation dynamics of lithium iodide", Journal of Chemical Physics 142, 044303 (2015)
  H. Schmidt, J. von Vangerow, F. Stienkemeier, A. Bogomolov, A. V. Baklanov, D. M. Reich, W. Skomorowski, C. P. Koch, M. Mudrich
  
• "A simple photoionization scheme for characterizing electron and ion spectrometers", Review of Scientific Instruments 87, 083105 (2016)
  A. Wituschek, J. von Vangerow, J. Grzesiak, F. Stienkemeier, and M. Mudrich
  
• "Desorption Dynamics of Rb2 Molecules Off the Surface of Helium Nanodroplets", Journal of Physical Chemistry A 120, 7641 (2016)
  A. Sieg, J. von Vangerow, F. Stienkemeier, O. Dulieu, and M. Mudrich
  
• "Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine", Physical Chemistry Chemical Physics 18, 18896 (2016)
  J. von Vangerow, A. S. Bogomolov, N. V. Dozmorov, D. Schomas, F. Stienkemeier, A. V. Baklanov and M. Mudrich