Vibronic interactions in s-trans-butadiene

Configuration interaction calculations are performed to investigate vibronic effects in s-trans-butadiene. Explicit calculations of vibronic coupling matrix elements find that their absolute value depends to a large extent on the level of theory used, a situation that differs markedly from that of many other physical quantities connected to spectroscopic properties. It is tentatively suggested that a scaling factor exists between calculations at relatively high and low levels of theory. The influence of the vibronic interactions on spectroscopic properties is evaluated and it is shown that a sizeable amount of valence rotation must occur upon excitation to S1(21Ag-).