Driving forbidden vibrational transitions in O₂⁺

Some vibrational transitions in molecules have the potential to serve as optical clocks or as probes for new physics.[1] The vibrational overtones in homonuclear molecules such as O₂⁺ are electric-dipole forbidden and thus intrinsically narrow and immune from some systematic shifts.[2] Here, we present our experimental investigations of these overtones in a pulsed molecular beam. Photoionization of the beam's cold neutral molecules produces state-selected molecular ions, while dissociation and time-of-flight mass spectrometry provide detection. Our goal is to reduce the measurement uncertainty in the vibrational frequency with the beam apparatus before moving to high-precision spectroscopy in an ion trap.

[1] D. Hanneke, B. Kuzhan, A. Lunstad, Optical clocks based on molecular vibrations as probes of variation of the proton-to-electron mass ratio, Quantum Science and Technology 6, 014005 (2021) 10.1088/2058-9565/abc863

[2] R. Carollo, A. Frenett, D. Hanneke, Two-Photon Vibrational Transitions in ¹⁶O₂⁺ as Probes of Variation of the Proton-to-Electron Mass Ratio, Atoms 7, 1 (2018) 10.3390/atoms7010001

This work is supported by the NSF (RUI PHY-1806223).