Stereoselectivity of cis–trans photoisomerization in ethylene: The significance of symmetry breaking minimum energy conical intersection

Abstract

This work finds that there are eight distinguished symmetry breaking minimum energy conical intersections (MECIs) between the N/V states of ethylene, in which the first four of them are closer to the reactant configuration than the remaining four. Consequently, the initially excited ethylene has a higher probability to relax to the first four MECIs or their adjacent configurations. Moreover, the ground potential energy surface around the first four MECIs has an asymmetric peaked topology and tilts toward the reactant configuration. Therefore, the cis–trans photoisomerization reaction in ethylene can exhibit the stereoselectivity of returning more back to the reactant rather than forming the product. In addition, the geometry–electronic structure relation and the geometric phase effect associated with a conical intersection were demonstrated by employing the adiabatic-to-diabatic analysis, in which the complete active space self-consistent-field wave function is represented by the equivalent covalent and ionic valence bond functions.