Credit: © 2010 ACS

Determining the arrangement of the atomic constituents of molecules is vital to many aspects of chemistry and has been mostly solved by various advances in spectroscopy and crystallography. Recent developments have made it possible for such analyses to be more direct: for example, atomic force microscopy has been used to image the bonding within molecules. Uncovering how different molecules interact with one another, however, is more problematic, and proving the presence of such non-covalent bonding has been restricted to indirect inference. Now Stefan Tautz and colleagues at Forschungszentrum Jülich in Germany, have shown that intermolecular bonds can be directly imaged using scanning tunnelling hydrogen microscopy (STHM), a variant of STM whereby the probe tip is sensitized with molecular hydrogen (J. Am. Chem. Soc. 132, 11864–11865; 2010).

They studied the behaviour of 3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) on a gold surface first using conventional STM, which shows how the molecules are arranged, and then using STHM. The STHM images (pictured) gave more detail than the conventional images, revealing not only various features of the molecular structure, but also a pattern of lines between the molecules. These originate at oxygen and hydrogen atoms and align well with expected intermolecular interactions. The physical basis for why this technique is able to produce such clear images of intermolecular interactions is, however, yet to be understood.

The original version of this story first appeared on the Research Highlights section of the Nature Chemistry website.