Observations were made in Dubna in the early 1960s for the temperature
dependence of fusion yields in muon catalyzed dd fusion ;
this was a strange phenomenon at the time since nuclear reactions of the
MeV scale appeared to be affected by the target temperature which is of the
meV scale. An Estonian graduate student, Vesman, proposed a resonant
process for muonic molecular formation to explain the
observations . According to the Vesman mechanism,
Muonic molecular ions are three-body systems interacting with both electromagnetic and strong forces, but to a good approximation ( eV), direct effects of the strong force can be neglected in calculating energy levels of loosely bound states, although other nuclear properties such as the charge form factors and polarizabilities play non-negligible roles. Now modern calculations have achieved amazing accuracies, as discussed in Section 2.1. Table 1.3 shows the nonrelativistic Coulomb bound state energy levels of muonic molecules.
The molecular complex is metastable, and can decay into several channels. An Auger transition of the molecule is an important step, which stabilizes the molecule, leading to fusion. This competes with the back decay process, which returns the excited molecular complex to and YZ. The details of the formation and back decay processes are discussed further in Section 2.2 and in Appendix B.