Observation of vibrational overtones by single molecule resonant photodissociation

Molecular ions sympathetically cooled by a chain of laser-cooled atomic ions are ideal for performing high-precision molecular spectroscopy with applications in astrochemistry and fundamental physics. The same system can be coupled with a broadband laser to perform survey spectroscopy and discover new molecular transitions. Here we present our results using three-ion chains of Ca$^{+}$ and CaH$^{+}$ to observe vibrational transitions via resonance enhanced multiphoton dissociation detected by Ca$^{+}$ fluorescence [1]. Based on theoretical calculations, the observed peaks are assigned to two vibrational overtones corresponding to transitions from the ground vibrational state, $\nu \quad =$ 0, to the excited vibrational states, $\nu \quad =$ 9 and $\nu \quad =$10. Our method allows us to track single molecular events, and it can be extended to handle any molecule by monitoring normal mode frequency shifts to detect the dissociation. [1] N. B. Khanyile, G. Shu, and K. R. Brown, Nat. Comm.~\textbf{6}, 7825~(2015)