Brown University confirms relativity reshapes chemical bonds in heavy elements
Original: Einstein's relativity rules chemical bonds in heavy elements, new research shows
Why This Matters
Confirms that relativistic quantum effects physically alter chemical bonding in heavy elements, with implications for materials science and chemistry education.
Brown University chemists published direct experimental evidence in Science showing that Einstein's theory of relativity disrupts the classic triple-bond structure in heavy elements like bismuth. Using photoelectron spectroscopy, the team demonstrated that relativistic spin-orbit coupling blurs the boundary between sigma and pi bonds.
Brown University researchers have provided the first direct spectroscopic evidence that the textbook model of triple chemical bonding breaks down in heavy elements. Published in the journal Science, the study was led by Professor Lai-Sheng Wang and Ph.D. students Deniz Kahraman and Jie Hui.
In lighter elements, a triple bond consists of one sigma bond (a strong head-on bond) and two pi bonds (weaker side-by-side bonds). However, in heavy elements like bismuth—located next to lead on the periodic table—the large nuclear mass causes orbiting electrons to travel at a significant fraction of the speed of light, bringing Einstein's relativistic effects into play.
At these speeds, an electron's spin and its orbital motion become coupled, a phenomenon known as spin-orbit coupling. This coupling disrupts the strict separation between sigma and pi bonds. The team formed carbon-bismuth molecules, cooled them to near absolute zero, and analyzed them with photoelectron spectroscopy, which uses a laser to eject electrons and measure their binding energy. The resulting spectrum revealed a bonding structure of one pi bond and two hybrid sigma-pi bonds—inconsistent with the classical triple-bond picture.
'The boundary between a sigma bond and a pi bond is now sort of smeared,' said Wang. 'We still have three bonds, but we don't really strictly have a sigma or a pi anymore.' Wang noted that while the theoretical idea has existed since the 1970s, this study provides the first direct experimental confirmation.