A quantum theory of chemical processes and reaction rates based on diabatic electronic functions coupled in an external field

Byline: Gustavo A. Arteca (1,2), O. Tapia (3) Keywords: diabatic functions; reaction rates; transition states; quantum states; external fields Abstract: The method discussed in this work provides a theoretical framework where simple chemical reactions resemble any other standard quantum process, i.e., a transition in quantum state mediated by the electromagnetic field. In our approach, quantum states are represented as a superposition of electronic diabatic basis functions, whose amplitudes can be modulated by the field and by the external control of nuclear configurations. Using a one-dimensional three-state model system, we show how chemical structure and dynamics can be represented in terms of these control parameters, and propose an algorithm to compute the reaction probabilities. Our analysis of effective energy barriers generalizes previous ideas on structural similarity between reactant, and product, and transition states using the geometry of conventional reaction paths. In the present context, exceptions to empirical rules such as the Hammond postulate appear as effects induced by the environment that supplies the external field acting on the quantum system. Author Affiliation: (1) Deepartement de Chimie et Biochimie, Laurentian University, Ramsey Lake Road, Sudbury, Ontario (2) Canada P3E 2C6 and Department of Physical Chemistry, Uppsala University, Box 579, S-751 23, Uppsala, Sweden (3) Department of Physical Chemistry, Uppsala University, Box 579, S-751 23, Uppsala, Sweden Article History: Registration Date: 03/12/2004 Received Date: 04/09/2004