Water molecules exist in two different forms with almost identical physical properties. For the first time, researchers have succeeded in separating the two forms to show that they can exhibit different chemical reactivities. These results were reported by researchers from the University of Basel and their colleagues in Hamburg in the scientific journal Nature Communications (“Observation of different reactivities of para and ortho-water towards trapped diazenylium ions”).

From a chemical perspective, water is a molecule in which a single oxygen atom is linked to two hydrogen atoms. It is less well known that water exists in two different forms (isomers) at the molecular level. The difference lies in the relative orientation of the nuclear spins of the two hydrogen atoms. Depending on whether the spins are aligned in the same or opposite direction, one refers to ortho- or para-water.