Watching chemistry in motion: Chemical environments mapped using molecular vibrations

Scientists have long known that a molecule's behavior depends on its environment. Taking advantage of this phenomenon, a group of researchers at the University of Chicago developed a new technique to map microscopic environments using the vibrations of molecules.

"It's a special new advance that will be broadly useful in studies of molecular and materials phenomena," said Andrei Tokmakoff, the Henry G. Gale Distinguished Service Professor in Chemistry at UChicago. He and two of his associates report their new technique in a paper published online in the journal Optics Express.

The new technique builds on ultrafast two-dimensional infrared spectroscopy, which emerged approximately 15 years ago as a method to probe molecular vibrations. When a laser pulse strikes a molecule, parts of its energy is transferred into the vibrations of the molecule. The ability of each single molecule to get rid of this excess energy, or relax, depends on the neighbors' ability to accept such energy. Thus molecules in different environments will relax at different rates, which are then used to determine the environment of individual molecules. Combining two-dimensional spectroscopy with a microscope enabled the researchers to directly visualize the microscopic variations in chemical environments.