I know the answer. It is from homework. It is about tritium atom in its ground state which turns into He+. It says that right after the reaction, the wave function remains as that ot the tritium. The question is: what are tha allowed energies of the system right after the reaction? Well, I understand that the wave functoin right after reation is that of ground state of tritium (which is just as for H-atom), but it is not an eigen state of the system because the system is He+ system. So, what are really the allowed energies of the system? I guess the wave function can be expanded as eigen states of He+. So, does it means that the allowed energies will be those of He+? Thanks!