Sweating the small stuff Home

A Water Molecule's Chemical Formula
is Really Not H20

A water molecule's chemical formula is really not H2O, at least from the perspective of neutrons and electrons interacting with the molecule for only attoseconds (less than 10>-15 seconds). According to new and recent experiments, neutrons and electrons colliding with water for just attoseconds will see a ratio of hydrogen to oxygen of roughly 1.5 to 1, so a more accurate formula for water under these circumstances would be H1.5O.

According to the experimenters (Aris Chatzidimitriou-Dreismann, Technical University-Berlin, dreismann@chem.TU-Berlin.de, 011-49-30-314-22692), this "opening of the attosecond time window" may be revealing dramatic quantum effects that were once too short-lived to catch. Nonetheless, such effects may revise conventional textbook notions of water and other everyday molecules.

Moreover, these experiments can provide new insights on chemical reactions at the 100-500 attosecond scale: the neutron and electron probes break apart the chemical bonds in molecules, as compared to laser-based attosecond studies, which have just ejected electrons from atoms at this point.

The story begins in 1995. At the ISIS neutron spallation facility in the UK, a German-British collaboration collided epithermal neutrons (those with energies of up to a few hundred electron volts) with a target that included water molecules (Chatzidimitriou-Dreismann et al., Physical Review Letters, 13 October 1997).

Detecting the number and energy loss of the scattered neutrons in the resulting attosecond-scale collisions, the researchers noticed that neutrons were scattering from 25% fewer protons than expected. Apparently, the protons in hydrogen were sometimes "invisible" to the neutron probes. While the exact details are still being debated by theorists, the researchers' own theoretical considerations suggest the presence of short-lived (sub-femtosecond) entanglement, in which protons in adjacent hydrogen atoms (and possibly the surrounding electrons) are all interlinked in such a way as to change the nature of the scattering results.

Realizing that water itself has anomalous properties, the researchers repeated the neutron experiments in other more typical molecules, for instance in benzene (conventionally noted as C6H6). In that case, they found that the neutrons saw a ratio of hydrogen to carbon of 4.5 to 6!

Meanwhile, this effect was also confirmed in various hydrogen-containing metals, in a collaboration with Uppsala University in Sweden. Now, the researchers (with new colleagues in Australia) have decided to use an independent experimental method to verify this effect.

In experiments at Australian National University in Canberra, the researchers used electron probes instead of neutrons, as the two particles interact with protons via fundamentally different forces (strong and electromagnetic interactions). Scattering electrons from a solid polymer called formvar (with basic building block C8H14O2), they observed the exact same shortfall in scattered electrons from hydrogen nuclei, comparable to the shortfall of scattered neutrons in accompanying neutron experiments on the same polymer.

This supports the earlier results on water and other systems. (Chatzidimitriou-Dreismann et al., Physical Review Letters, 1 August 2003)

--Physics News Update