  The comprehension of nonadiabatic dynamics in polyatomic systems relies
heavily on the simultaneous advancements in theoretical and experimental
domains. The gas-phase electron diffraction (GUED) technique has attracted
widespread attention as a promising tool for observing the photochemical and
photophysical features at all-atomic level with high temporal and spatial
resolutions. In this work, the GUED spectra were predicted to perform a
double-blind test of accuracy in excited-state simulation for cyclobutanone
based on the trajectory surface hopping method, with respect to the benchmark
data obtained by upcoming MeV-GUED experiments at the Stanfold Linear
Accelerator Laboratory. The results show that the ultrafast nonadiabatic
dynamics occurs in the photoinduced dynamics, and two C2 and C3 channels play
dominant roles in the nonadiabatic reactions of cyclobutanone. The simulated
UED signal can be directly interpreted by atomic movements, providing a unique
view to monitor the time-dependent evolution of the molecular structure in the
femtosecond dynamics.
