Splat prints of floppy molecules.

Splat prints of floppy molecules

A molecule's geometric shape is one of its most fundamental properties, but many molecules are difficult to characterize geometrically, especially those held together loosely or having absorbed enough energy to be in a highly excited state. Researchers from the Weizmann Institute of Science in Rehovot, Israel, and the Argonne (Ill.) National Laboratory have developed a technique that yields geometrical images of individual molecules -- no matter how floppy or excited.

The method, called Coulomb explosion imaging, takes advantage of the large electrical repulsion between the nuclei within molecules rapidly stripped of all or most of their electrons. To get an image, the researchers first accelerate a beam of molecules to a velocity about 2 percent that of the speed of light, then smash them into a foil of solid material only 30 angstroms thick. The foil strips electrons from the molecules but allows the nuclei to pass through unscathed. Like an exploding shell, the stripped molecule flies apart as a detector records the speed and direction of each fragment. From that information, the researchers can calculate the original arrangement of the nuclei in the molecule.

The group has already used the technique to reveal the structure of positively charged methane ions and other carbon-based ions. It also works with neutral molecules if an extra electron is added to each molecule to make it easier to accelerate and then removed later.