H<sub>2</sub>O or H<sub>1.5</sub>O? Water Mystery Solved

No matter how long you look at it, a water molecule is still just two hydrogens latched onto one oxygen.

So says a new experiment, which contradicts a previous claim that water lost at least half of a hydrogen - effectively becoming H1.5O - when looked at with an extremely fast "camera."

This camera uses subatomic particles, called neutrons, to probe molecular structure. When a beam of neutrons is shot into a water target, the way that the neutrons scatter into different directions gives a picture of the molecules.

The "exposure" of the camera - the time that the neutrons take to bounce off of a water molecule - is less than a femtosecond, or one quadrillionth of a second.

An earlier experiment found that the neutrons scattered as if there were only one and a half hydrogens to every oxygen. These surprising results were explained by assuming that the two hydrogens are very briefly "entangled" with each other.

The entanglement effectively blurs the borders between the hydrogens, so they scatter less neutrons than expected. As exposure time increases, the blurring disappears - in something called quantum decoherence - and the two separate hydrogens become visible.

But new neutron pictures taken at Rensselaer Polytechnic Institute find two hydrogens even with exposure times of as little as 0.001 femtoseconds. At this shorter timescale, theory would have expected to see fewer hydrogens if entanglement truly was occurring.

This research - re-affirming the universality of "H2O" - is described in the 13 May issue of Physical Review Letters.

Related Stories