Einstein's relativity rules chemical bonds in heavy elements, new research shows

Brown University chemists have provided direct evidence that Einstein's theory of relativity alters the structure of triple chemical bonds in heavy elements, according to a study published in Science. The research team, led by professor of chemistry Lai-Sheng Wang, used photoelectron spectroscopy to analyze bonds between carbon and bismuth. Wang said the idea that relativity is important in heavy elements has been around since the 1970s, but the study shows direct spectroscopic evidence that textbook descriptions of chemical bonding are not true for heavy elements. Textbook triple bonding involves one sigma bond and two pi bonds. However, in heavy elements, increased nuclear mass causes electrons to speed up to a significant fraction of the speed of light, where relativistic effects such as spin-orbit coupling disrupt the strict separation between sigma and pi bonds. Wang said the boundary between a sigma bond and a pi bond is smeared, resulting in three bonds that are not strictly sigma or pi. The photoelectron spectrum showed the carbon-bismuth bonds fit a structure of one pi bond and two hybrid sigma-pi bonds. Wang said the experimental verification may spur a rewriting of chemistry textbooks as heavy elements like bismuth gain research interest for applications in solar cells and quantum computing. The work was funded by the U.S. National Science Foundation and the U.S. Department of Energy.