Speaker
Description
Accurate energy intervals in light open-shell atoms remain a stringent test for both precision spectroscopy and ab initio electronic-structure theory. One of the most persistent benchmarks is neutral boron: the separation between the ground $^2P^o$ state and the lowest $^4P^e$ quartet, together with the quartet fine structure, has resisted definitive theoretical--experimental reconciliation for decades. In this work we report high-precision all-particle calculations using massive explicitly correlated Gaussian expansions and include leading relativistic and quantum-electrodynamics contributions through order $\alpha^4$. We determine the $^2P^o \rightarrow ^4P^e$ excitation energy in $^{11}$B as 28967.65(7) cm$^{-1}$, achieving sub-0.1 cm$^{-1}$ accuracy and resolving the long-standing ambiguity in this interval. Beyond the gross separation, we predict the fine-structure splittings within the $^4P^e$ manifold, providing a concrete target pattern for future spectroscopic searches for a state that has thus far largely eluded observation. These results remove a key remaining uncertainty in the boron spectrum and establish a new benchmark for quantifying electron correlation and relativistic/QED effects in few-electron, open-shell atomic systems.