Bernd Abel (Leipzig University) in cooperation with A. Spesyvyi, J. Žabka, M. Polášek, F. Postberg, and A. Charvat
Abstract: Small ice particles play an important role in atmospheric and interstellar chemistry. Here we present an apparatus for the generation of low-intensity beams of single mass selected charged water particles in vacuum. They are produced via electrospray ionization of water at atmospheric pressure and undergo evaporative cooling when transferred to vacuum through an atmospheric vacuum interface. M/z selection was achieved through two subsequent quadrupole mass filters operated in the variable frequency mode within a range of m/z values between 8×10^4 and 3×10^7. Velocity and charge of the selected particles are measured using a non-destructive single pass image charge detector. From the known electrostatic acceleration potentials and settings of the quadrupoles the particle masses could be obtained and accurately be controlled. It has been shown that the droplets are frozen within the transit time of the apparatus such that ice particles are present after the quadrupole stages and finally detected. The demonstrated correspondence between particle mass and specific quadrupoles potentials in this device allows to prepare beams of single particles with a repetition rate between 0.1-1 Hz with various diameter distributions from 50 to 1000 nm at 30 to 250 eV of kinetic energy per charge. This corresponds to kinetic energies and particle masses quickly available between 600m/s (80nm) and 50m/s (900nm) and particle charge numbers between 103-104[e], depending upon size. A concept and timescale for post-accelerating particles up to 4-5 km/s will be given.
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