Formation of translationally cold MgH+ and MgD+ molecules in an ion trap -: art. no. 011401

We have produced and cooled the molecular ions MgH+ and MgD+ in a linear Paul trap. These ions were generated by the photochemical reactions Mg+(3p P-2(3/2)) + H-2 (D-2)-->MgH+ (MgD+) + H (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 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.