High-Resolution Spectroscopy of {R}ydberg Molecular States of ⁸⁵{R}b₂ Near the 5s+7p 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 $^{85}$Rb$_2$. The observed line structure is modeled using precise ground-state positions and a lower bound of $\tau > 1.1 \times 10^{-9}$ s is set on the excited-state autoionization lifetime.