Multiple-State Nonadiabatic Dynamics Simulation of Photoisomerization of Acetylacetone with the Direct ab Initio QTMF Approach.

In the present work, the quantum trajectory mean-field (QTMF) approach is numerically implemented by ab initio calculation at the level of the complete active space self-consistent field, which is used to simulate photoisomerization of acetylacetone at ∼265 nm. The simulated results shed light on the possible nonadiabatic pathways from the S2 state and mechanism of the photoisomerization. The in-plane proton transfer and the subsequent S2 → S1 transition through the E-S2 /S1 -1 intersection region is the predominant route to the S1 state. Meanwhile, rotational isomerization occurs in the S2 state, which is followed by internal conversion to the S1 state in the vicinity of the E-S2 /S1 -2 conical intersection. As a minor pathway, the direct S2 → S1 → S0 transition can take place via the E-S2 /S1 /S0 three-state intersection region. The rotamerization in the S1 state was determined to be the key step for formation of nonchelated enolic isomers. The final formation yield is predicted to be 0.57 within the simulated period. The time constant for the S2 proton transfer was experimentally inferred to be ∼70.0 fs in the gas phase and ∼50.0 fs in dioxane, acetonitrile, and n-hexane, which is well-reproduced by the present QTMF simulation. The S1 lifetime of 2.11 ps simulated here is in excellent agreement with the experimentally inferred values of 2.12, 2.13, and 2.25 ps in n-hexane, acetonitrile, and dioxane, respectively. The present study provides clear evidence that a direct ab initio QTMF approach is a reliable tool for simulating multiple-state nonadiabatic dynamics processes.