The elusive Element 61, promethium, part of the lanthanide series, has finally had its bound form characterized thanks to the effort of scientists at the Department of Energy’s Oak Ridge National Laboratory (ORNL) and the National Institute of Standards and Technology (NIST). Despite being long discovered in 1945, promethium remained an enigma in its bound state until recently, as researchers successfully synthesized a coordination complex and determined its electronic structure. The findings, significant for understanding promethium's properties and potential technology applications, were published in Nature.
Commonly found in many of the devices that define contemporary life - from smartphones to spacecraft batteries - the promethium's characterization as a part of these rare earth elements seemed almost overdue. The shortcoming in knowledge persisted partly due to promethium's short half-life of just 2 ½ years, making its stable form challenging to study. As Dmytro Bykov, a theoretical chemist at ORNL, stated, "Since the discovery of the periodic law, we have had a good understanding of all the elements, but that doesn’t change the fact that you need to experiment to confirm that understanding."
To tackle the enigmatic nature of promethium's electrons, researchers used X-ray absorption spectroscopy alongside the computational prowess of ORNL's IBM AC922 supercomputer Summit. The Director's Discretionary Program granted the team time on this formidable machine, housed at the Oak Ridge Leadership Computing Facility - a Department of Energy Office of Science user facility. The integration of experimental and computational methods allowed for a more holistic depiction of the element's electronic structure than either approach could have accomplished alone.
Bykov underscored the effort's grounding in experimental science saying, "the most important thing is that the team purified and characterized the element in the bound form. But the cherry on top is that we were able to run these simulations for a deeper understanding of the experimental observations." Capturing the essence of promethium's structure involved solving the complex Schrödinger equation, which describes the probabilistic waves of behavior in electrons. This work not only fills a gap in the lanthanide series' knowledge base but also extends the frontier of quantum chemistry's application in material science.
