We report the observation and analysis of the $3\,^3\Pi_{ \Omega}$ double-minimum electronic excited state of $^{ 39}$K$^{ 85}$Rb. The spin-orbit components ($0^{ +}, 0^{ -}, 1$ and 2) of this state are investigated based on potentials developed from the available \emph{ ab initio} potential curves. We have assigned the vibrational levels $v'=2-11$ of the $3\,^3\Pi_{ 1,2}$ potentials and $v'=2-12$ of the $3\,^3\Pi_{ 0^{ +/-}}$ potential. We compare our experimental observations of the $3\,^3\Pi_{ \Omega}$ state with predictions based on theoretical potentials. The observations are based on resonance enhanced multiphoton ionization (REMPI) of ultracold KRb in vibrational levels $v"=14-25$ of the $a\,^3\Sigma^+$ state. These \emph{ a}-state ultracold molecules are formed by photoassociation of ultracold $^{ 39}$K and $^{ 85}$Rb atoms to the 5(1) state of KRb followed by spontaneous emission to the \emph{ a} state.
Categories: physics.atom-ph quant-ph