High-resolution spectroscopy of Rydberg molecular states of Rb 2 85 near the 5 s + 7 p asymptote

Rydberg molecules, often exemplified by long-range ``trilobite'' molecules, are a subject of much recent interest at high principal quantum number $n$. States that use the same bonding mechanism can exist at much lower $n$ and less-extreme internuclear separations that are still quite long range. We use a high-resolution pulsed amplifier to study previously detected transitions to a low-$n$ Rydberg molecular state near the $5s+7p$ asymptote in $^{85}\mathrm{Rb}_{2}$. The observed line structure is modeled using precise ground-state positions and a lower bound of $\ensuremath{\tau}g1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ s is set on the excited-state autoionization lifetime.