Chemists observe distribution of electrons in a single molecule
Chemists at Utrecht University and their colleagues at the Institute of Physics of the Czech Republic have for the first time observed the distribution of electrons in a single molecule. The electron distribution in a molecule is a major factor in determining the process of chemical reactions. "In fact, we now have all of the tools we need to directly observe individual chemical reactions between two molecules", according to Dr. Ingmar Swart, supervising the research team at Utrecht University. Until now, researchers could only derive information about the progress of a reaction indirectly from information about a minimum of dozens of molecules. The results of their research will be published in Nature Communications on 27 May 2016.
The best microscopes available only permit researchers to observe a single molecule; it is impossible to zoom in on the distribution of electrons. So the researchers from Utrecht and Prague inventively utilised a discovery from earlier research into observing a molecule using an Atomic Force Microscope (AFM). An AFM 'feels' the surface of the molecule to be studied using a 'needle' whose apex consists of a single atom. In the previous study, which was published in Physics Review Letters, the researchers discovered that the distribution of charge in the front most atom causes the molecules to appear distorted in AFM images. In this new study, the researchers show that these distortions can be exploited to determine the charge distribution.
Two snapshots
To do so, the researchers made two snapshots: one with an electrically neutral tip apex, and one with a slightly charged front atom. The charged tip responded to the electron distribution in the molecule and provided a different image than the neutral tip did. The distribution of the electronic charge could be calculated with atomic resolution based on the difference between these two images. The results of the experimental observations agree well with Density Functional Theory calculations (DFT), the theory used to calculate the electronic structure of larger molecules.
Predicting and controlling chemical reactions
Eventually, the researchers hope to initiate a chemical reaction between two molecules and observe it as it occurs. Swart: "By moving one molecule towards another in a controlled manner, we can see the exact moment when they sense one another and the processes that their interaction initiate. This will undoubtedly provide new insights that will allow us to better predict and control chemical reactions. That would be interesting, because it could make existing chemical production processes cleaner and more efficient."
This study was financed in part by an ECHO-Stip subsidy provided by NWO as part of the Physics and Chemistry Sector Plan.
Reference
Mapping the electrostatic force field of single molecules from high-resolution scanning probe images, Nature Communications, 27 May 2016. DOI: 10.1038/ncomms11560