Correction to the binding energy of (dtμ) meso molecules

The non‐relativistic Coulomb binding energy of (dtμ) has been cited as 666.0 meV. Spin, finite‐size and relativistic corrections, treated as perturbations, lower this by about 10%. It is pointed out that for lightly bound systems, perturbation theory needs correction, an effect known in nuclear physics. In the present case, the change is about 0.6 meV. This is significant since energies are quoted to 0.1 meV accuracy.