15min:

XIN TONG, MATTHIAS GERMANN AND STEFAN WILLITSCH, Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.

Cold molecular ions prepared by sympathetic cooling with laser-cooled ions in an ion trap represent attractive systems for new spectroscopic experiments. The long trapping times (up to hours) and state lifetimes (up to minutes) in an almost perturbation-free environment enable the long interaction times required for the study of forbidden spectroscopic transitions which have not been accessible before in molecular ions.

Here, we present a proof-of-principle experiment for the investigation of dipole-forbidden infrared transitions in cold N₂⁺ ions using quantum-cascade-laser technology in combination with action spectroscopy. Because sympathetic-cooling experiments typically use small ensembles of tens to hundreds of ions, the confinement of their population into a single quantum state is essential to improve the sensitivity of our experiments. This is achieved by state-selective generation of the ions using threshold photoionization followed by sympathetic cooling.

Finally, we discuss the experimental requirements for performing highly sensitive spectroscopic measurements on trapped, cold molecular ions and present an outlook on current developments which employ quantum-logic methods for non-destructive spectroscopic studies on single sympathetically cold molecular ions.\footnoteJ.~Mur-Petit, J.~J.~Carcia-Ripoll and S.~Willitsch et al. Phys.~Rev.~A \underline\textbf85, 022308 2012.