Taming molecular ions: from cold chemistry to fundamental physics

Broadband optical pumping of trapped molecular ions offers unique opportunities for characterizing trace species, controlling and studying chemical reactions over the full range of rotational energies, and state preparation for precision measurements. First demonstrated a decade ago with ground rotational state preparation of AlH⁺, this technique has recently been extended to include the oxide SiO⁺. Furthermore, it has been generalized to produce steady-state, narrowly distributed rotational populations in SiO⁺ with arbitrary rotational quanta. With this flexible control now available, we report, for the first time, a chemical reaction involving a reactant with extreme rotational excitation and its kinetic characterization. In particular, we reveal a surprising enhancement of the hydrogen abstraction reaction SiO⁺ + H₂ → SiOH⁺ + H when SiO⁺ is in “super rotor” states, with rotational quantum numbers as high as 170. Time permitting, I will also discuss how this newly developed tool for generating narrowly distributed, steady-state rotational distributions can be applied to efficiently characterize radioactive polyatomic ion candidates for precision measurement.