Observation of vibrational overtones by single molecule resonant photodissociation

Molecular ions can be held in a chain of laser-cooled atomic ions by sympathetic cooling. This system is ideal for performing high-precision molecular spectroscopy with applications in astrochemistry and fundamental physics. Here we show that this same system can be coupled with a broadband laser to discover new molecular transitions. We use three-ion chains of Ca${}^{+}$ and CaH${}^{+}$ to observe vibrational transitions via resonance enhanced multiphoton dissociation detected by Ca${}^{+}$ fluorescence. Based on theoretical calculations, we assign the observed peaks to the transition from the ground vibrational state, $\nu =0$, to $\nu =9$ and $\nu =10$. Our method allows us to track single molecular events, and it can be extended to work with any molecule by using normal mode frequency shifts to detect the dissociation. This survey spectroscopy serves as a bridge to the precision spectroscopy required for molecular ion control.