Production of ultracold diatomic and triatomic molecular ions of spectroscopic and astrophysical interest

We have produced large samples of ultracold (<20 mK) ArH+, ArD+, N2H+, N2D+, H3+, D3+, D2+, H2D+ and D2D+ molecular ions, by sympathetic cooling and crystallization via laser-cooled Be+ ions in a linear radio-frequency trap. As technique, we used chemical reactions with sympathetically cooled noble gas atomic ions or N2+ and O2+ molecular ions. These ultracold molecules are interesting targets for high-precision measurements in fundamental physics and may open new routes for the study of state-selective chemical reactions relevant to interstellar chemistry.