A Rice University laboratory has improved upon its ability to determine molecular structures in three dimensions in ways that challenge long-used standards.
By measuring the vibrations between atoms using femtosecond-long laser pulses, the Rice lab of chemist Junrong Zheng is able to discern the positions of atoms within molecules without the restrictions imposed by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) imaging.
The technique can capture the structure of molecules at room temperature or very low or high temperatures and in many kinds of samples, including crystals, powders, gels, liquids and gases. It will be useful to scientists who study catalysis, energy storage, organic solar cells and biomembranes, among many other possibilities, Zheng said.
The researchers reported their results online this week in the American Chemical Society’s Journal of Physical Chemistry.
Zheng and his co-authors at Rice and Oak Ridge National Laboratory analyzed variations of a model molecule, 4′-methyl-2’nitroacetanilide (MNA), and compared the results with computer-generated and XRD models. The images matched nicely, he said.
Traditional spectrometers read the wavelengths of light scattered by samples to identify materials and study their properties. But the one-of-a-kind spectrometer developed by Zheng uses very short laser pulses to read the vibrational energies inherent to every atom. Those energies determine how atoms bond to form a molecule, and a measurement of the length and angles of those bonds can be extracted from the vibrations themselves, he said.
The infrared and terahertz lasers used for the experiment captured information about a molecular angle in a mere 100 femtoseconds.
“The important part of this paper is to demonstrate that our method can determine three-dimensional molecular structures no matter whether they’re in liquids or solids,” Zheng said.
Read more at: Phys.org