During the past 15 years or so, scientists have developed quite a knack for cooling and controlling beams of atoms--leading to atom lasers, atom interferometry, and Bose-Einstein condensates. But molecules have been much more unyielding. They possess complex energy structures relative to atoms and have access to huge numbers of molecular rotational-vibrational states, all of which make it difficult to apply atom-cooling methods to molecules.

Yet some success in cooling molecules to within fractions of a degree above absolute zero has been reported recently. For example, physics professor Gerard Meijer and coworkers at the University of Nijmegen and at the FOM Institute for Plasma Physics, Rijnhuizen, devised a method in which a series of pulsed electric fields causes molecules to lose kinetic energy in multiple stages. The technique, which can be applied to any molecule with an electric dipole moment, has been used to prepare millikelvin-temperature pulses of deuterated ammonia molecules in a single quantum state.

Now, Meijer and coworkers Floris M. H. Crompvoets, Hendrick L. Bethlem, and Rienk T. Jongma have gone an important step further by developing a storage ring into which decelerated bunches of molecules can be injected for further study. Storage rings enable researchers to repeatedly probe molecules with light or particle beams at well-defined times and locations and may eventually be used to study collisions between counterpropagating beams of neutral molecules.

RINGING IN MOLECULES Physicists in the Netherlands slow ammonia molecules emitted from a pulsed valve to a near stand-still using an electrostatic device known as a Stark decelerator. Packets of neutral molecules emerge from the decelerator in a single quantum state and are collimated and injected into a hexapole torus storage ring (orange), where they can be probed repeatedly with lasers (blue) or used in other investigations.

[Previous Story] [Next Story]

Top

Chemical & Engineering News
Copyright © 2001 American Chemical Society