Ultracold molecular ions

FURTHER CONNECTIONS AND DIRECTIONS 5.3.1 Ultracold Molecular Ions... 

Roth, B., Koelemeij, J.C.J., Daerr, H., Ernsting, L, Jorgensen, S., Okhapkin, M., Wicht, A., Nevsky, A., and Schiller, S., Trapped ultracold molecular ions Candidates for an optical molecular clock for a fundamental physics mission in space, in Proc. of the 6th Intemat Conf. on Space Optics, ESTEC, Noordwijk, The Netherlands, ESA-SP 621,2006. 

Finally connections to ultracold molecular ions, to tests of fundamental laws, to quantum computing with ultracold polar molecules, to ultracold collisions and chemistry, and to more speculative areas are mentioned. 

There are a variety of in situ experiments (spectroscopy) planned which are of fundamental importance for characterizing such a trap for creating brilliant beams of ultracold molecular ions, including biomolecules (e.g. from an electrospray ion source). It is also possible to synthesize directly in the trap special ions such as clusters or molecules with van der Waals bound ligands. More details, e.g. how to record a pure rotational spectnun of ultracold CHjf ions, are discussed in Chapter 6. 

Chapter 18 of this book, by Roth and Schiller, is an extensive discussion of cold molecular ions. One topic that is not discussed, however, is the possibility of forming untrapped molecular ions at ultracold temperatures and low densities by photoionization of ultracold neutral molecules formed by PA or MA. Indeed, as discussed above, the ionization of ultracold neutral molecules has already been extensively used for... 

Roth, B., Blythe, R, Daerr, H., Ratacchini, L., and Schiller, S., Production of ultracold diatomic and triatomic molecular ions of spectroscopic and astrophysical interest, J. Phys. B At. Mol. Opt. Phys., 39, S1241 2006. 

A quite different problem impeding the study of cold chemical reactions in ion crystals is the internal energy of the stored ions. While Coulomb interactions are very efficient at sympathetically cooling translation, the internal degrees of freedom of molecular ions are not coupled to the laser cooled atomic ions. The creation of ultracold ions in rf traps is further discussed in Chapter 6. 

Cooling all degrees of freedom of molecular ions down to a few K or even in the sub-K range has many obvious applications in spectroscopy. One example is to study rotational transitions in floppy molecular ions such as CHg. Applications of rf traps in the analysis of molecular structures together with planned extensions towards infrared or microwave absorption spectroscopy on ultracold ions are discussed in Chapter 6. 

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