A New Study is the First to Separate and React Water’s Two Molecular Forms

Water molecules are ubiquitous, vital, and may have the world’s most well-known chemical formula (H₂O). The properties of water are quite unique; its solid state is less dense than its liquid state, raising pressure lowers its melting point, and it exists as a liquid at room temperature despite low molecular mass. Even more unique is the water molecule’s ability to exist as two distinct nuclear configurations called spin isomers.

The two spin isomers of water molecules differ based on the direction of the nuclear spin of the two hydrogen nuclei. If the two hydrogen nuclei have parallel spins, the molecule is known as ortho-water. If the two hydrogen nuclei have opposite spins, the molecule is known as para-water. Water at room temperature always contains a mix of these two spin isomers and, until recently, it has been nearly impossible to study them separately.

Now a study co-authored by Stefan Willitsch at the University of Basel has successfully isolated the two forms of water and found that they vary in performance of certain chemical reactions. [1] The group used electric field technology to isolate ortho- and para-water molecules and then reacted these with ultracold diazenylium ions (N₂H⁺). This reaction is similar to what might occur in interstellar space, where diazenylium ions interact with water molecules to form nitrogen molecules (N₂) and hydronium ions (H₃O⁺). [1]

The successful separation of these isomers in this work holds great promise for future research. For example, ability to produce a water sample with specific nuclear spin could greatly improve the sensitivity of nuclear magnetic resonance methods. [2] Scientists can also work toward understanding how the two isomers differ physically and chemically. The results of this study showed that para-water reacted 25% faster than ortho-water with diazenylium. [1] This research provides insight into the chemical reactivity of water at temperatures near absolute zero, and may be especially impactful for astrochemistry and the study of pre-stellar clouds.

References:
^{[1] https://www.nature.com/articles/s41467-018-04483-3
[2] https://physicsworld.com/a/water-isomers-separated-by-spin/}