Ultrafast PEPICO Spectroscopy of Electron Correlation Effects and Nonadiabatic Population Transfer Between HOMO-Excited and HOMO-1-Excited States in Acetone and Methyl Azide

We employ ultrafast pump-probe spectroscopy with photoelectron-photoion coincidence (PEPICO) detection to observe the complex dynamics of highly excited states of acetone and methyl azide. Both molecules are excited by an 8.0 eV photon to a mixed character Rydberg-valence excited state, then probed with 1.6, 3.2, or 4.8 eV photons to ionize from the excited state. Methyl azide shows 25 fs population transfer from a strongly mixed-character state to a pure valence state, and ab-initio multiple spawning (AIMS) calculations reveal that the transfer is driven by strong nonadiabatic coupling through a conical intersection seam well above the minimum energy conical intersection. Acetone exhibits a very fast decay to a state with mixed Rydberg-valence character. This state then decays in 330 fs predominantly by internal conversion to a pure 3s Rydberg state.