Quantum mechanics of electro-nuclear systems towards a theory of chemical reactions

A new electronuclear separability approach is used to split global translational motion from the molecular hamiltonian (H-m) and to define state dependent molecular frames; an operator is obtained coupling the global translational momentum to the operators for linear momenta of nuclei and electrons. The method prompts for a different and hopefully sounder description of chemical processes. The electronic wave functions do not depend upon the instantaneous nuclear positions; they determine stationary geometric arrangements of sources of external Coulomb potential. For processes conserving charge and particle number, such as those intervening in a chemical reaction, reactants and products are eigenstates of H-m with momenta quantized by taking the system to be in a volume V with periodic boundary conditions. The physical and chemical processes are represented by changes in populations among the eigenstates of H-m. Such changes must be produced by a coupling to an external field (e.g. electromagnetic). One of the very new results is that chemical processes may even be affected by sound fields. Quantum mechanical conservation principles enter in a natural manner to describe chemical processes. They help define selection rules. in particular, parity plays a central role. If both reactant and product channels have the same parity, the theory requires the existence of a transition structure with different parity to mediate the interconversion. This rule is important since most of the chemical reactions in the ground electronic states of reactants and products belong to this class. Chemical processes can be described in the same general terms as Franck-Condon spectroscopy.