Flash-freezing of molecular ions in a storage ring
This kind of laboratory astrophysics helps to understand in more detail the physical and chemical properties of cold interstellar matter.
The interaction of molecular ions with free electrons is of key importance to understand the physical and chemical properties of cold astrophysical environments like interstellar molecular clouds. Whereas electron-ion recombination has been studied in great detail in storage ring and ion trap experiments in the last two decades, information about the exchange of energy between slow electrons and the internal motion (rotation and vibration) of molecular ions was rather limited.
Researchers of the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, of the Weizmann Institute of Science in Rehovot (Israel) and of three other collaborating institutions have now published first quantitative results for fast electron cooling of rotating singly charged HD molecular ions. In the TSR heavy ion storage ring of the MPIK an HD molecular ion beam was merged with cold electrons of 33 K (-240°C) temperature, i. e. 33 degrees above absolute zero.
The interaction with the electrons reduced the rotational temperature of the ions from initially about 1200°C to -150°C within only 8 seconds and stabilized it at this low value in the simultaneously acting thermal radiation field at the ambient room temperature (300 K). During the process, the ions pass the electron cooling bath about 175000 times per second. The cooling due to so-called superelastic collisions, where some amount of energy is transferred from the rotational motion of the ion to linear motion of the electron, is well described by theoretical calculations initiated through this experiment.
Prof. Dr. Andreas Wolf
Max Planck Institute for Nuclear Physics, Heidelberg
Prof. Dr. Daniel Zajfman
Weizmann Institute of Science, Rehovot, Israel
http://link.aps.org/doi/10.1103/PhysRevLett.102.223202 Orginal publication
http://www.mpi-hd.mpg.de/blaum/members/molecular-qd/index.en.html Group of Prof. Andreas Wolf
http://www.weizmann.ac.il/particle/molecule/ Group of Prof. Daniel Zajfman
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