Analysis of Symmetry in Chemical Reactions.
PURDUE UNIV LAFAYETTE IND PROJECT SQUID HEADQUARTERS
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The authors investigated the effect of the symmetry of the electronic and nuclear motion in chemical reactions. The analysis focuses on concerted reactions which are defined to be describable by a single transition matrix. The transition matrix for rearrangement collisions is derived in a quasiadiabatic representation of electronic motion such that the electronic degrees of freedom of reactants and products can be defined separately. Three alternative forms are obtained for the transition matrix from which symmetry rules are derived. Five approximations are applied Separate conservation of total electronic spin Neglect of virtual electronic transitions Born-Oppenheimer approximation Fixed nuclear configuration Franck-Condon-type approximation Neglect of remaining effects of dynamics. The five approximations lead to an expression for the transition matrix from which Shulers rules and the Woodward-Hoffman rules follow by application of the Wigner-Eckart theorem. The inapplicability of one or more of these approximations are discussed. Physical reasons are presented for the wide applicability of the Woodward-Hoffmann rules. It is suggested that the principle of maximum bonding proposed by Woodward and Hoffmann is a useful rule, but not supported by theory and experiment as a principle. Author
- Atomic and Molecular Physics and Spectroscopy