Book of Abstracts Book of Abstracts - Universität Konstanz

Photoionization Dynamics of Pure Helium Droplets
Darcy S. Peterka 1,2 , Jeong Hyun Kim 2 , Chia Wang 1 , Musahid Ahmed 2 , Daniel M. Neumark 1,2
B - 25
1 College of Chemistry, University of California, Berkeley, Address, Berkeley, 94720, USA
2 Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, Ca
94720, USA
Helium nanodroplets have been demonstrated to provide a unique environment for
spectroscopic studies. Their ability to capture and cool foreign dopants in a controlled way has
led to their description as an "ultracold nanolaboratory". Many groups have used this property to
their advantage, performing rotational and vibrational spectroscopic studies in great detail, with
slightly less work being done by probing electronic transitions. However, there is almost no
work on the photoionization of pure clusters. We have studied the single photon vacuum
ultraviolet ionization of pure helium droplets below the atomic helium ionization threshold
using velocity-mapped photoelectron imaging. We see wavelength dependant changes in the
ionization dynamics of the droplet. Below the atomic threshold, indirect processes are the
dominant source of electrons, leading to electrons of very low kinetic energy 1 . With photon
energies larger than the Helium atom ionization energy, direct ionization to Hen + takes place,
giving fast photoelectrons.
References
[1] D. S. Peterka, A. Lindinger, L. Poisson, M. Ahmed, and D.M. Neumark, Phys. Rev. Lett. 91,
043401 (2003).
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