Vibronic symmetry correlation in molecular combination and dissociation

Abstract

The principle of conservation of vibronic symmetry in molecular combination and dissociation is discussed. It leads to the aufbau of the vibronic (vs purely electronic) states of polyatomic molecules. Methods to construct composite vibrational (and vibronic) wavefunctions from those of molecular fragments (reactants or products or transition complexes) are described. These vibronic functions, constructed from local site symmetry, will have the overall symmetry of the point group that is preserved throughout the reaction and will possess the correct dissociation limit. The construction of a composite vibrational wavefunction is illustrated by using a symmetrically and collinearly dissociating X₂Y₂ molecule. The theory of vibronic correlation is applied to the recently observed production of excited formaldehyde (and its chemiluminescence) from the reaction of O₂(¹Δ_g) with olefins. This theory promises one a qualitative way to conceive the possible vibronic excitation of reactants and products in a chemical reaction.