Formation of translationally cold MgH+/MgD+ molecules in an ion trap

A. Bertelsen, Ivan R. Vogelius, Solvejg J�rgensen +2 more

Roland Wester

Kristian Speranza Mølhave, Michael Drewsen

We have produced and cooled the molecular ions ${\mathrm{MgH}}^{+}$ and ${\mathrm{MgD}}^{+}$ in a linear Paul trap. These ions were generated by the photochemical reactions ${\mathrm{Mg}}^{+}{(3p}^{2}{P}_{3/2})+{\mathrm{H}}_{2} ({\mathrm{D}}_{2})\ensuremath{\rightarrow}{\mathrm{MgH}}^{+} ({\mathrm{MgD}}^{+})+\mathrm{H} (\mathrm{D}),$ and identified by the radial separation in the trap of ions with different charge-to-mass ratios. The molecular translational motion was cooled sympathetically by Coulomb interaction with laser-cooled ${\mathrm{Mg}}^{+}$ ions to a temperature estimated to be below 100 mK. Ordered structures (ion crystals) containing more than 1000 ions, with more than $95%$ being molecular ions, were obtained. Such translationally cold and well-localized samples of molecular ions could become very useful for molecular physics and chemistry.

Anders Kragh Hansen, Peter Frøhlich Staanum, Klaus Højbjerre +5 more

Working with MgH+molecular ions in a linear Paul trap, we routinely cool their translational degrees of freedom by sympathetic cooling with Doppler laser cooled Mg+ions. Giving the time for the molecules to equilibrate internally to room temperature blackbody radiation, the vibrational degree of freedom is frozen out, leaving only the rotational degree of freedom to be cooled. We have implemented a new technique for laser-induced rotational ground-state cooling of vibrationally and translationally cold MgH+ions, using a scheme based on excitation of a single rovibrational transition. This technique is generalizable to any diatomic polar molecular ion, given an appropriate mid-infrared laser source such as a quantum cascade laser.

Klaus Højbjerre, Anders Kragh Hansen, Peter Sandegaard Skyt +2 more

The first steps toward the implementation of a simple scheme for rotational cooling of MgH + ions based on rotational state optical pumping is considered. The various aspects of such an experiment are described in detail, and the rotational state-selective dissociation spectra of translationally and vibrationally cold MgH + ions are presented, with and without the optical pumping laser being present. While rotational cooling is as yet not evident, first results showed evidence of a change in the rotational distribution in the presence of the optical pumping laser.

Joan P. Marler