Rotationally Resolved Spectroscopy of a Single Polyatomic Molecular Ion*

We report the first rotationally resolved spectrum of a single polyatomic molecular ion in the gas phase. Building upon the recently developed inelastic recoil spectroscopy (IRS) technique, we have achieved a spectral resolution sufficient to observe the resolved rotational-vibrational transitions of a wide range of trapped analyte molecular ions. The high precision of IRS shown in this work presents an attractive platform for astrochemistry, single molecule chiral detection, and tests of fundamental physics including parity violation in the electroweak force.