Lowest Excitation Energy of 9Be

Abstract

Variational calculations employing explicitly correlated Gaussian functions and explicitly including the nuclear motion [i.e., without assuming the Born-Oppenheimer (BO) approximation] have been performed to determine the lowest singlet transition energy in the 9Be atom. The non-BO wave functions were used to calculate the 2 relativistic corrections ( 1=137:035 999 679). With those corrections and with the 3 and 4 QED corrections determined previously by others, we obtained 54 677:35 cm 1 for the 31S ! 21S transition energy. This result falls within the error bracket for the experimental transition of 54 677:26 10 cm 1. This is the first time an electronic transition of Be has been calculated from first principles with the experimental accuracy