Inelastic fine-structure transfer efficiency in CaO+ collisions

Determine the efficiency of inelastic, state-changing collisions that transfer CaO+ between the Ω=1/2 and Ω=3/2 fine-structure manifolds under the experimental conditions, including their ability to transfer population across the 130 cm−1 spin–orbit gap.

Background

The rotational-state model assumes that collisions with background gas reset the molecular internal state at the estimated Langevin collision rate and that the post-collision state follows a Boltzmann distribution. However, radiative transitions between the Ω=1/2 and Ω=3/2 fine-structure manifolds are electric-dipole-forbidden, so population transfer between these manifolds requires inelastic, state-changing collisions. The efficiency of this process affects the predicted rotational-state dynamics and the interpretation of the dipole-phonon signal lifetimes.

Existing estimates for rotational quenching in cold helium buffer-gas systems indicate that quenching occurs only once per approximately 10–100 collisions, but those estimates do not establish the transfer rate across the 130 cm−1 spin–orbit gap in CaO+ under the conditions of the trapped-ion experiment.