New research published on March 3, 2025, reveals groundbreaking insights on the electronic structure of the radioactive molecule radium monofluoride (RaF). This study, featured in Nature Communications, provides highly precise calculations of its excited electronic states, offering new avenues for research across chemical and nuclear physics disciplines.
Radium monofluoride, composed of the radioactive element radium, has long captivated the attention of physicists, especially as it acts as a sensitive probe for new physics. The study conducted at the CERN-ISOLDE facility focused on the spectroscopic analysis of the 14 lowest excited electronic states of RaF, achieving remarkable agreement of 99.64% with state-of-the-art relativistic Fock-space coupled cluster calculations.
“The precision of our findings showcases the accuracy of the computational methods we employed. It highlights the capability of relativistic quantum chemistry to tackle complex systems, even those as challenging as radioactive molecules,” noted the authors of the article.
The research addressed the inherent difficulties presented by radium isotopes, which have short half-lives—most ranging from nanoseconds to mere days. Only 226Ra and 228Ra possess longer half-lives of 1600 years and 5.75 years, respectively, allowing for more extensive experimental investigations.
Through laser spectroscopy techniques, the team successfully observed excited states of RaF, establishing precise excitation energies. Notably, the spectrum showed a new transition identified near the predicted value of 16,615 cm−1. This transition was ascribed to the C2Σ1/2 state, providing clear evidence for the effectiveness of ab initio theories when applied to such complex molecular systems.
Further refinements to earlier assignment methods were validated, leading to the reassignment of several transitions. For example, the transition observed at 15,142.7 cm−1 was updated from (B2Δ3/2) to (B2Δ5/2), aligning with predicted values.
The high energy levels observed also shed light on the roles played by electron correlation and quantum electrodynamics (QED) effects, both of which were determined to be significant across all excited states of RaF.
Dr. G. N. from the CERN research team elaborated on these findings. He stated, “By enhancing laser cooling methods and utilizing our comprehensive electronic structure calculations, we are now poised to perform tests for symmetry-violations and potential discrepancies with established physics models.”
The advancement of observational techniques at high energies allowed scientists to probe the multi-reference characters of several states. This opens possibilities to explore molecular constants, aiding future pursuits to identify molecular properties potentially indicative of new physics.
The successful implementation of relativistic coupled-cluster methods marks this research as pivotal for future studies involving heavy atoms and radioactive species. The researchers’ approach not only defines new benchmarks for precision measurements but facilitates important dialogues around the physics governing heavier elements.
Inside the rigorous computational framework applied throughout the study, every calculation was geared toward optimizing accuracy, ensuring results fell within 12 meV of experimental observations. Such precision is necessary for continued exploration of potential symmetry violations, as quantum transitions involving heavy atoms like radium hold the promise of unlocking fundamental mysteries within particle physics.
Looking toward the future, the team aims to extend their research beyond the initial 30,000 cm−1 range, paving the way for the detailed mapping of RaF’s electronic structure. They suggest additional studies can yield fascinating insights, particularly concerning Rydberg series convergence and core-valence interactions.
This research signifies not just advancements within quantum chemistry but stands as a bridge leading to potential scientific breakthroughs capable of challenging established notions, urging scientists to reconsider boundaries of the Standard Model as they explore the universe's fundamental laws.”