  Simulations of photochemical reaction dynamics have been a challenge to the
theoretical chemistry community for some time. In an effort to determine the
predictive character of current approaches, we predict the results of an
upcoming ultrafast diffraction experiment on the photodynamics of cyclobutanone
after excitation to the lowest lying Rydberg state (S$_2$). A picosecond of
nonadiabatic dynamics is described with ab initio multiple spawning. We use
both time dependent density functional theory and equation-of-motion coupled
cluster for the underlying electronic structure theory. We find that the
lifetime of the S$_2$ state is more than a picosecond (with both TDDFT and
EOM-CCSD). The predicted UED spectrum exhibits numerous structural features,
but weak time dependence over the course of the simulations.
