An MRD CI investigation of the photochemical isomerization of cyclohexadiene to hexatriene

Abstract

The photoisomerization of cyclohexadiene to cis-hexatriene has been investigated using the multi-reference configuration interaction (MRD CI) method involving all active valence electrons. It has been determined that the initial absorption process in cyclohexadiene is nonvertical, and that the excitation energy and oscillator strength obtained are in good agreement with gas phase absorption measurements. The excited state which is initially populated in the absorption process can undergo rapid nonradiative relaxation to a lower-lying excited state with a barrierless potential leading to formation of the ground state hexatriene photoproduct. The large absorption linewidth which is experimentally observed is correlated with rapid nonradiative relaxation in the excited state which is both photophysical and photochemical in nature. The effect of orbital symmetry upon the reaction, as well as the dipole moments of the excited states are also discussed.