Chemistry Department Seminar

The spectroscopy of the low-lying singlet states of butadiene has been a vexing problem for theorists for over forty years. The positions of the lowest-lying singlet states at the ground state geometry are something of a methodological Rorschach test and the planar stationary points of these states have seen modest attention. Important work has been done on the ultrafast dynamics of butadiene following excitation to the bright 11Bu but these studies are often forced to use simple wavefunctions that may lead to exaggerated couplings. We present new simulation results of its electronic spectrum based on Equations of Motion Coupled Cluster Theory in large basis sets using a vibronic coupling model involving many vibrational modes. We investigate the sensitivity of the results to the choice of vibronically-coupled states and test the dependence of the results on vertical excitation energies. We believe that butadiene should be considered somewhat less vexing than it has been before and our results can be used as a starting point for accurate explorations of its short-time excited state dynamics.