Oct. 21, 2010 Chemical reactions tend to slow down as temperature is lowered, but this isn't always true. Deborah Jin,Jun Ye, and their colleagues at the National Institute of Standards and Technology (NIST) and the University of Colorado have shown that chemical reactions can continue even at temperatures just a fraction of a degree above absolute zero.
In recent experiments, they took diatomic potassium and rubidium molecules, each in their ground states (lowest-possible energy), and found that when mixed, the molecules dissociated and combined into KRb -- molecules with one potassium and one rubidium atom.
Furthermore, the reaction rates could be slowed considerably by applying an electric field, which orients the molecules in such a way as to suppress chemical reactions. The reason for this is that the KRb molecules are fermions and obey the Pauli Exclusion Principle, just like where two electrons of the same quantum energy and spin are forbidden to lie in a single quantum state -- just operated at the level of whole molecules. When applied electric fields oriented the KRb molecules so as to have the same spin state (they would already have the same energy state, being in the ground state to start with) chemical reactions were greatly suppressed.
NIST physicist John Bohn has now provided the theoretical underpinnings for the ultracold chemical behavior. He will describe how spin-dependent chemistry, or "stereodynamics," will operate in future experiments.
The Presentation, "Manipulation of Ultracold Chemistry," takes place on Oct. 28 at the Frontiers in Optics (FiO) 2010/Laser Science XXVI -- the 94th annual meeting of the Optical Society (OSA), which is being held together with the annual meeting of the American Physical Society (APS) Division of Laser Science at the Rochester Riverside Convention Center in Rochester, N.Y., from Oct. 24-28.
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