Two-Photon Vibrational Transitions in O$_2^+$ as Probes of Variation of the Proton-to-Electron Mass Ratio

Molecular vibrations provide sensitive probes for variation of the proton-to-electron mass ratio $\mu$. The O$_2^+$ molecule has many vibrational overtone transitions that appear capable of detecting change at the $10^{-18}$ level or better [1]. Here we report calculations of two-photon transition rates, systematic effects, and achievable statistical precision for measurements using these overtones. We present results of state preparation via photoionization and progress towards driving the transitions and detection via photodissociation. [1] R. Carollo, A. Frenett, D. Hanneke, Atoms v.7, 1 (2019)