We simulate the photodynamics of gas-phase cyclobutanone excited to the S2 state using fewest switches surface hopping (FSSH) dynamics powered by time-dependent density functional theory (TDDFT). We predict a total C3+C2 photoproduct yield of 9%, with a C3:C2 product ratio of 1:8. Two primary S2→S1 conical intersections are identified: β stretch and CCH bend, with the higher energy β stretch being associated with sub-picosecond S2 decay. Excited state lifetimes computed with respect to electronic state populations were found to be 7.0 ps (S2→S1) and 550 fs (S1→S0). We also generate time-resolved difference pair distribution functions (ΔPDFs) from our TDDFT-FSSH dynamics results in order to generate direct comparisons to ultrafast electron diffraction experiment observables. Global and target analysis of time-resolved ΔPDFs produced a distinct set of lifetimes: i) a 0.462 ps decay, and ii) a 16.8 ps decay that both resemble the S2 minimum, as well as iii) a long (> nanosecond) decay that resembles the S1 minimum geometry and the fully separated C3/C2 products. Finally, we contextualize our results by considering the impact of the most likely sources of significant errors.
@article{arxiv.2402.10336,
title = {Ultrafast Photochemistry and Electron Diffraction for Cyclobutanone in the S2 State: Surface Hopping with Time-Dependent Density Functional Theory},
author = {Ericka Roy Miller and Sean J. Hoehn and Abhijith Kumar and Dehua Jiang and Shane M. Parker},
journal= {arXiv preprint arXiv:2402.10336},
year = {2024}
}