A CASSCF/MRCI Trajectory Surface Hopping Simulation of the Photochemical Dynamics and the Gas Phase Ultrafast Electron Diffraction Patterns of Cyclobutanone

TL;DR

This study uses advanced quantum chemical methods and trajectory surface hopping to simulate cyclobutanone's photochemical reactions, revealing primary dissociation pathways and linking structural dynamics to ultrafast electron diffraction patterns.

Contribution

It presents a comprehensive simulation of cyclobutanone's photodissociation, integrating nonadiabatic effects and providing detailed mechanistic insights and experimental correlations.

Findings

Reproduces primary dissociation channels with specific product ratios.

Most trajectories reach ground state within 200 fs, dissociation completes by 300 fs.

Minimal impact of triplet states on the reaction mechanism within the observed timescale.

Abstract

We present the simulation of the photochemical dynamics of cyclobutanone induced by the excitation of the 3s Rydberg state. For this purpose, we apply the complete active space self-consistent field method together with spin-orbit multireference configuration interaction singles treatment, combined with the trajectory surface hopping for inclusion of the nonadiabatic effects. The simulations were performed in the spin-adiabatic representation including nine electronic states derived from three singlet and two triplet spin-diabatic states. Our simulations reproduce the two previously observed primary dissociation channels: the C2 pathway yielding C2H4 + CH2CO and the C3 pathway producing c-C3H6 + CO. In addition, two secondary products, CH2 + CO from the C2 pathway and C3H6 from the C3 pathway, both of them previously reported, are also observed in our simulation. We determine the ratio of the C3:C2 products to be about 2.8. Our findings show that most of the trajectories reach their electronic ground state within 200 fs, with dissociation events finished after 300 fs. We also identify the minimum energy conical intersections that are responsible for the relaxation and provide an analysis of the photochemical reaction mechanism based on multidimensional scaling. Furthermore, we demonstrate a minimal impact of triplet states on the photodissociation mechanism within the observed timescale. In order to provide a direct link to experiments, we simulate the gas phase ultrafast electron diffraction patterns and connect their features to the underlying structural dynamics.