This article focuses on isomerizations of molecules, i.e. chemical reactions during which a molecule is transformed into another one with the same atoms but in a different spatial configuration. We consider the special case in which the system breaks into two submolecules whose internal geometry is solid during the whole procedure. We prove, under some conditions, that the distance between the two submolecules stays bounded during the entire reaction. This paper generalizes [6] in two directions. The first one is that we relax the assumptions that the ground state eigenspaces of the submolecules have to fulfill. The second one is that we allow semirelativistic kinetic energy as well
