Imaging Excited-State Dynamics of Doped He Nanodroplets in Real-Time

Abstract

The real-time dynamics of excited alkali metal atoms (Rb) attached to quantum fluid He nanodroplets is investigated using femtosecond imaging spectroscopy and time-dependent density functional theory. We disentangle the competing dynamics of desorption of excited Rb atoms off the He droplet surface and solvation inside the droplet interior as the Rb atom is ionized. For Rb excited to the 5p and 6p states, desorption occurs on starkly differing time scales (∼100 versus ∼1 ps, respectively). The comparison between theory and experiment indicates that desorption proceeds either impulsively (6p) or in a transition regime between impulsive dissociation and complex desorption (5p).

Femtosecond photoexcitation dynamics inside a quantum solvent

“…Therefore, we use TDDFT modeling of the photoexcitation process in order to distinguish these two contributions. Previously, TDDFT simulations could only be compared to time-dependent experiments at the weakly-interacting droplet surface 16 . In the interior, the dopant-He interaction is much stronger, with the consequence that significantly more excess energy (270 meV ≈ 2200 cm −1 in our case) is coupled into the system during photoexcitation, challenging the accuracy of the TDDFT approach.…”

“…In the last years, the approach of TDDFT for the bosonic system of helium has been successfully applied to describe the dynamical interaction of surface- and center-located species with the helium quantum fluid, providing important insight into effects like superfluidity on the microscopic level 26 , desorption dynamics 16 , or collision processes 27 , 28 .…”

“…This will, however, require a detailed knowledge about the response of the quantum fluid to the photoexcitation of a dopant atom or molecule. So far, only the ultrafast dynamics in pure helium droplets have been studied 14 , and femtosecond measurements on doped helium droplets were restricted to the surface-bound alkali metals 15 , 16 that can hardly couple to helium bubble modes. Since most foreign atoms and molecules reside inside the droplets and couple more strongly, we have concentrated on the electronic excitation of single atoms well inside the droplets.…”

Cold physics and chemistry: Collisions, ionization and reactions inside helium nanodroplets close to zero K

“…Videos of the HND dynamics for a Rb dopant that is first excited and then ionized can be found in the Supporting Information of Ref. [91]. Here, the interplay between the heliophobic Rb* and the heliophilic Rb + and the timescales between excitations govern the overall dynamics.…”

Capture of Xe and Ar atoms by quantized vortices in4He nanodroplets

“…where T [r] is the kinetic energy of a fictitious system of noninteracting particles (with mass m 4 ) constituting a BEC in the present case. As in recent applications of the TDDFT approach, 23,[26][27][28][29][30] we use the correlation energy density functional E c proposed in ref. 31.…”