Charging and ion ejection dynamics of large helium nanodroplets exposed to intense femtosecond soft xray pulses

Journal Article · Wed Dec 01 04:00:00 EST 2021 · European Physical Journal. Special Topics

DOI:https://doi.org/10.1140/epjs/s11734-021-00280-0· OSTI ID:1846301

Saladrigas, Catherine A.; Feinberg, Alexandra J; Ziemkiewicz, Michael P; Bacellar, Camila; Bucher, Maximilian; Bernando, Charles; Carron, Sebastian; Chatterley, Adam S; Decker, Franz-Josef; Ferguson, Ken R.; Bostedt, Christoph

Ion ejection from charged helium nanodroplets exposed to intense femtosecond soft X-ray pulses is studied by single-pulse ion time-of-flight (TOF) spectroscopy in coincidence with small-angle X-ray scattering. Scattering images encode the droplet size and absolute photon flux incident on each droplet, while ion TOF spectra are used to determine the maximum ion kinetic energy, Ekin, of He+ j fragments (j = 1-4). Measurements span HeN droplet sizes between N similar to 10(7) and similar to 10(10) (radii R-0 = 78-578 nm), and droplet charges between similar to 9x10(-5) and similar to 3x10(-3) e/atom. Conditions encompass a wide range of ionization and expansion regimes, from departure of all photoelectrons from the droplet, leading to pure Coulomb explosion, to substantial electron trapping by the electrostatic potential of the charged droplet, indicating the onset of hydrodynamic expansion. The unique combination of absolute Xray intensities, droplet sizes, and ion Ekin on an event-by-event basis reveals a detailed picture of the correlations between the ionization conditions and the ejection dynamics of the ionic fragments. The maximum E-kin of He+ is found to be governed by Coulomb repulsion from unscreened cations across all expansion regimes. The impact of ion-atom interactions resulting from the relatively low charge densities is increasingly relevant with less electron trapping. The findings are consistent with the emergence of a charged spherical shell around a quasineutral plasma core as the degree of ionization increases. The results demonstrate a complex relationship between measured ion E-kin and droplet ionization conditions that can only be disentangled through the use of coincident single-pulse TOF and scattering data.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE Office of Science; Swiss National Science Foundation (SNSF); SLAC National Accelerator Laboratory; USDOE Office of Science - Office of Basic Energy Sciences - Chemical Sciences, Geosciences, and Biosciences Division; National Science Foundation (NSF); Deutsche Forschungsgemeinschaft (DFG)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1846301
• Journal Information: European Physical Journal. Special Topics, Journal Name: European Physical Journal. Special Topics Journal Issue: 23 Vol. 230; ISSN 1951-6355
• Country of Publication: United States
• Language: English

Related Subjects

Helium
Ion
injection