Ultra-cool Molecules - Complex systems coming to a standstill
This goes way beyond freezing: Only in the last few years have scientists been able to cool atoms close to absolute zero, that is zero Kelvin or -273 degree Celsius. In this state they transform into a so-called Bose-Einstein-condensate with unique properties and can be used for measurements of extraordinary precision. For the first time, scientists at the Ludwig-Maximilians-Universität (LMU) Munich and other European institutions have been able to transfer this cooling method in computer simulations directly to molecules and therefore much more complex systems. In the science journal Physical Review Letters, the team reports how ultra-cold molecules could be generated with a novel application of laser light. The scientists now hope for insights into chemical reactions as well as new interactions and effects.
Not only ultra-cold atoms but also molecules close to zero Kelvin are extraordinary research objects. These were previously thought to be too complex to be cooled by optical methods, that is through laser light. Molecules consist of many atoms and therefore show internal degrees of freedom as well as external motion – and cooling essentially means the slowing down of movement. “Internal motion generates unwanted heating effects which cannot be easily avoided”, explains team leader Regina de Vivie-Riedle. This explains why it has only been possible to cool atoms and in that state bring them together to form molecules.
In contrast, the novel application would allow the simultaneous cooling of external and internal motion. This method combines laser light with an optical resonator, a system consisting of two special mirrors. In the gap between these two mirrors all states of a molecule can be controlled by laser light which reduces motion to a minimum. “Our results are based on modern quantum chemical simulations of a test molecule OH”, says de Vivie-Riedle. “They show that vibrations and rotations inside the molecule can be cooled down completely. At the same time external motion reaches a temperature of only a few micro-Kelvin. Our approach opens new perspectives for the preparation and control of ultra-cold complex systems.”
“Cavity cooling of internal molecular motion”,
Giovanna Morigi, Pepijn W.H. Pinkse, Markus Kowalewski, and Regina de Vivie-Riedle
Physical Review Letters, August 17, 2007 issue
Professor Dr. Regina de Vivie-Riedle
Department of Chemistry and Biochemistry, LMU Munich