Charging and ion ejection dynamics of large helium nanodroplets exposed to intense femtosecond soft X-ray pulses
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
- Univ. of Southern California, Los Angeles, CA (United States)
- Argonne National Lab. (ANL), Argonne, IL (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Technical Univ. of Berlin (Germany)
- California Lutheran Univ., Thousand Oaks, CA (United States)
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- SLAC National Accelerator Lab., Menlo Park, CA (United States); Technical Univ. of Berlin (Germany)
- Univ. of Southern California, Los Angeles, CA (United States); State Univ. of New York (SUNY), Adirondak, NY (United States)
- Technical Univ. of Berlin (Germany); Eidgenoessische Technische Hochschule (ETH), Zurich (Switzerland)
- Technical Univ. of Berlin (Germany)
- Argonne National Lab. (ANL), Argonne, IL (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Paul Scherrer Inst. (PSI), Villigen (Switzerland); Ecole Polytechnique Federale Lausanne (Switzerland)
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
We report 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~107 and ~1010 (radii R0 = 78–578 nm), and droplet charges between ~9×10-5 and ~3×10-3 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 X-ray 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 Ekin 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 Ekin and droplet ionization conditions that can only be disentangled through the use of coincident single-pulse TOF and scattering data.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF); German Research Foundation (DFG); Swiss National Science Foundation (SNSF)
- Grant/Contract Number:
- AC02-76SF00515; AC02-05CH11231; AC02-06CH11357; CHE-1664990; DMR-1701077; 718/14-2
- OSTI ID:
- 1872757
- Journal Information:
- European Physical Journal. Special Topics, Vol. 230, Issue 23; ISSN 1951-6355
- Publisher:
- SpringerCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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