Cooling a beam of molecular ions so that they occupy their lowest-energy quantum state (ground state) would permit high-precision study of their properties and would improve understanding of star-forming gas clouds. Now research teams in Sweden and Germany have accomplished this feat by placing the entire apparatus for trapping and probing molecular ions inside cryogenic cooling systems at temperatures of around 10 degrees above absolute zero. They expect to carry out experiments relevant for astrophysics at a new level of precision.
Reactions between cold atoms, molecules, and ions in interstellar clouds create the material from which stars and planets are made. The states of the molecules involved in these processes can be studied by measuring how the gas absorbs light from more distant stars, but to understand these spectra, researchers need data from laboratory measurements on cold molecules.
Molecular ions can be conveniently trapped by electromagnetic fields in storage rings, but cooling them to interstellar temperatures is challenging. If the ions are warmer, they occupy a mixture of their many vibrational and rotational states, so any measurements are averaged over those states and are hard to interpret. Ideally, researchers could cool them enough that the ions are exclusively in their ground state of rotation and vibration. “Well-defined initial states are essential for the interpretation,” says Henning Schmidt of Stockholm University, co-leader of DESIREE (Double Electrostatic Ion Ring Experiment).
Previous efforts to cool molecular ions have mostly used collisions with surrounding atoms of an inert cold gas such as helium [1]. But for reasons that are still not entirely clear, these methods failed to bring the ion temperature below about 20 K.
Sign up with Google
