ECAMP 15

A Multi-Reflectron Time-of-Flight (MR-ToF) device, originally developed through a collaboration between the TU Darmstadt and the University of Greifswald [1], has been adapted to trap multiply charged helium nanodroplets (HNDs) using purely electrostatic fields. The system enables confinement of the droplets for a mean lifetime of about 14 seconds, with individual droplets surviving for over a minute. Successful proof-of-principle measurements demonstrate efficient storage over thousands of revolutions. The achievable storage time is highly sensitive to the vacuum conditions and has been thoroughly characterized as a function of chamber pressure.
The multi-reflectron trap setup provides a versatile platform for investigating excitation-induced processes in doped helium nanodroplets, enabling both the study of weak transitions and time-resolved decay dynamics. Recently, Blackbody Infrared Radiative Dissociation (BIRD) experiments were successfully carried out using the devices vacuum chamber as a blackbody radiation source. These measurements revealed a significant reduction in the mean lifetime of the stored droplets when doped with water clusters. Excitation of intermolecular vibrational modes in the embedded clusters and subsequent heat transfer to the surrounding droplet leads to enhanced helium evaporation, eventually rendering the droplets undetectable as their kinetic energy falls below the detection threshold.
Additional plans for future developments include the integration of a pick-up electrode to monitor changes in charge, mass, and energy of the droplets over time. This implementation will enable novel calorimetric measurements at the nanoscale, providing insights into droplet thermodynamics as well as the possibility for measurements leading to a better understanding of the dynamics of pristine helium droplets, inspired by the work of Hanozin et al. [2], who observed significant charge loss and Rayleigh decay in aqueous droplets.

This research was funded in whole or in part by the Austrian Science Fund (FWF) [10.55776/I6221, 10.55776/V1035].

[1] Schlaich, M.; Fischer, J.; Fischer, P.; Klink, C.; Obertelli, A.; Schmidt, A.; Schweikhard, L.; Wienholtz, F. A Multi-Reflection Time-of-Flight Mass Spectrometer for the Offline Ion Source of the PUMA Experiment. Int. J. Mass Spectrom. 2024, 495, 117166. https://doi.org/10.1016/j.ijms.2023.117166.
[2] Hanozin, E.; Harper, C. C.; McPartlan, M. S.; Williams, E. R. Dynamics of Rayleigh Fission Processes in ∼100 Nm Charged Aqueous Nanodrops. ACS Cent. Sci. 2023, 9 (8), 1611–1622. https://doi.org/10.1021/acscentsci.3c00323.