Rotationally Cold OH− Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE

Abstract

We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of OH^{-} ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of 13.4±0.2 K with 94.9±0.3% of the ions in the rotational ground state. This is consistent with the storage ring temperature of 13.5±0.5 K as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an OH^{-} beam where 99.1±0.1% of approximately one million stored ions are in the J=0 rotational ground state. We measure the intrinsic lifetime of the J=1 rotational level to be 145±28 s.

Cryogenic merged-ion-beam experiments in DESIREE: Final-state-resolved mutual neutralization of Li+ and D−

“…This is virtually impossible for studies of collisions involving molecular or cluster ions. Thus, the present merged-beams experiment, together with the recent demonstration of a (near) single-quantum-state beam of molecular ions in the same apparatus [31], promise to open up a new era in the field of atomic and molecular collision physics. Worldwide there are three cryogenically cooled ion-beam storage rings in operation [27,33,34] where experiments with internally relaxed ions are performed [35].…”

“…Merged-beams studies provide a level of control over the collision energy which is not possible with other methods [29]. The storage in the cryogenic environment allows for control of the ions' internal excitation prior to their interactions by storing them for up to hours [30] and waiting for spontaneous relaxation or actively manipulating the distribution on quantum levels [31].…”

Mutual Neutralization of O− with O+ and Ruette1, Dochain2, Launoy3 et al. 2018Phys. Rev. Lett.Self Cite275100View full textAdd to dashboardCite

“…Such effects will almost always be a problem in merged beams experiments with molecular ions. At the DESIREE (Double Electrostatic Storage Ring Experiment) infrastructure at Stockholm University [41,42], beams of anions and cations can be stored for long times, relax to the lowest quantum states [43] and be merged for studies of mutual neutralization at very low temperatures and well defined collision energies. Our present studies with atomic reactants will serve to benchmark similar experiments conducted with DESIREE.…”

Roadmap on dynamics of molecules and clusters in the gas phase

“…with lasers) for experiments. The preparation of beams of small molecular ions with nearly all of them in a single ro-vibrational quantum state has been demonstrated for OH − at both CSR and DESIREE [195,196]. Diatomic molecules, such as OH − , have only one possible conformation, while larger molecules may have many different forms.…”