Water molecules have been separated according to the two possible spin orientations of the molecules' hydrogen atoms.

Water is a mixture of two isomers that differ in the direction of their hydrogen spins. The spins are parallel in 'ortho' water and antiparallel in 'para' water. Little is known about the physical and chemical differences between these two isomers because no viable separation method has been available.

Now Gil Alexandrowicz and his co-workers at the Technion–Israel Institute of Technology in Haifa report a procedure in which they shot a slow beam of water molecules through a strong magnetic field. The field acted like a selective lens for ortho water, which, unlike para water, is sensitive to a magnetic field. Purified ortho water was then collected through a small slit.

The work could pave the way for highly sensitive nuclear magnetic resonance experiments, which rely on the alignment of nuclear spins.

Science 331, 319–321 (2011)