Knowledge Bank

Over the past years, ultracold ($T\<10$~mK) atomic and molecular ions prepared by laser and sympathetic cooling in ion traps have found an increasing number of applications in molecular physics} {\bf 229} (2003), 203}, chemistry} {\bf 100} (2008), 043203} and spectroscopy} {\bf 309} (2005), 749}. At low temperatures the ions undergo a phase transition from a "gaseous" state to an ordered structure in the trap. Owing to their strong localisation single ions can be observed, addressed and manipulated opening up perspectives for new gas-phase experiments with single-particle sensitivity. In this talk, novel experimental schemes for reactive-scattering studies and high-resolution spectroscopy based on ultracold ions will be discussed. A new method to investigate reactive collisions between laser-cooled ions and velocity-selected neutral molecules will be introduced. The technique is particularly suited to measure ion-molecule reaction rates as a function of temperature down to $\approx 1$~K. First results on the Ca$+$ + CH$3$F~$\to$ CaF$+$ + CH$3$ reaction will be presented. In the second part of the talk, prospects for the state-selected generation of cold molecular ions and their application in high-resolution spectroscopic experiments will be explored.