FORMATION OF EXOTIC ATOMS BY DIRECT CAPTURE AND VIA TRANSFER FROM HYDROGEN

Exotic atoms like muonic atoms can be formed either by direct capture, often called Coulomb capture, or by muon transfer from a muonic hydro gen atom. The first estimates for the formation predicted, for both me chanisms, probabilities approximately proportional to the charge numbe r Z. The experiments did not confirm such a simple Z-dependence. In di rect capture, it turned out that the chemical bond played a decisive r ole, at least for lighter elements. In the formation via transfer, sur prising data were obtained not only for heteroatomic molecules but als o for noble gases. Whereas for direct capture, a model is able to repr oduce quite satisfactorily a great number of measured capture ratios, including those in hydrogen compounds, the formation via transfer seem s to put completely different and more fundamental questions.