Spectroscopy and dynamics of barium-doped helium nanodroplets

Abstract

Excitation spectra up to the ionization threshold are reported for barium atoms located on the surface of helium nanodroplets. For states with low principal quantum number, the resonances are substantially broadened and shifted towards higher energy with respect to the gas phase. This has been attributed to the repulsive interaction of the excited atom with the helium at the Franck-Condon region. In contrast, for states with high principal quantum number the resonances are narrower and shifted towards lower energies. Photoelectron and ZEKE spectroscopy reveal that the redshift results from a lowering of the ionization threshold due to polarization of the helium by the barium ionic core. As a result of the repulsive interaction with the helium, excited barium atoms desorb from the surface of the droplets. Only when excited to the 6s6p 1 P 1 state, which reveals an attractive interaction with the helium, the atoms remain attached to the droplets.

Picosecond solvation dynamics of alkali cations in superfluidHe4nanodroplets

“…This is thought to be the main reason for the difference between the experimental and theoretical results. This assumption is supported by the ZEKE spectra recorded for ground state and excited Ba atoms on helium droplets [62]. Here the reduction of the ionization threshold for the excited atom was about half of that found for the ground state configuration.…”

“…5. The experimental spectrum corresponding to ā N = 2700 droplet [62], which is also shown in this figure, has a long tail towards high energies. This tail has been attributed to the presence of autoionizing states in the continuum and consequently should not be considered when comparing to the calculations.…”

“…Besides being interesting by itself [62], the ZEKE spectrum probes the structure of the surface dimple state of the dopant atom and the accuracy of the He-cation ground state pair potential. Since the impurities are described classically and the electron orbitals are not explicitly included, the ZEKE spectrum is calculated from the semiclassical approximation of the vibrational Franck-Condon factors of an instantaneous transition from the neutral ground state to the ionic state.…”

Dynamics of solvation and desolvation of rubidium attached to He nanodroplets

“…Various recent experimental and theoretical studies have addressed the dynamics of solvation and desolvation of ionized or excited metal atoms off the surface of He nanodroplets [7,[12][13][14][15][16][17][18][19][20][21]. So far, these studies have concentrated on measuring the total yield and the final velocity of the ejected atoms as a function of the atomic species and the electronic state of excitation.…”

Communication: Nucleation of quantized vortex rings in 4He nanodroplets

“…DF calculations find this configuration to have the Ba atom residing in a dimple at the surface of the droplet, 31 in agreement with experiments. 32,33 Snapshots of the dynamical evolution of the Ba + @ 4 He 1000 system are presented in Fig. 2 (Multimedia view).…”