Regular Article

Fall-back time for photo-ionized Cs atoms attached to superfluid ⁴He nanodroplets^⋆

¹ Laboratoire des Collisions, Agrégats, Réactivité, IRSAMC, UMR 5589, CNRS et Université Paul Sabatier-Toulouse 3, 118 route de Narbonne, 31062 Toulouse Cedex 09, France
² Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
³ Departament FQA, Facultat de Fsica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
⁴ Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona, Spain
⁵ Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
⁶ Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, 79194 Freiburg, Germany

^a e-mail: marti@fqa.ub.edu

Received: 19 December 2018
Received in final form: 11 March 2019
Published online: 7 May 2019

Abstract

We have studied the dynamic evolution of a Cs atom photo-excited from 6s to 6p and 7s states on a helium droplet using time-dependent ⁴He-DFT simulations. Depending on the excited electronic state, the Cs impurity remains on the droplet surface or it is ejected. Upon subsequent photo-ionization of the excited Cs atom the resulting Cs⁺ cation may either be ejected or come back to the droplet, depending on the time delay between photo-excitation and photo-ionization. We have calculated the critical time delay separating these two different behaviors, as well as final ion velocities. These observables will be used for future comparison with planned pump-probe experiments.