Quantitative Modeling of Excited-State Dynamics in Valence Photoionized Vinyl Fluoride

Area of Science:

• Physical Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• Vinyl fluoride photoionization has long been debated.
• Understanding excited-state dynamics is crucial for chemical reaction pathways.

Purpose of the Study:

• To resolve long-standing debates on the dissociative photoionization of vinyl fluoride (fluoroethene).
• To provide quantitative predictions for experimental observables.

Main Methods:

• Employed large-scale surface-hopping ab initio molecular dynamics (SH-AIMD) simulations.
• Combined density functional theory (DFT) and complete active space second-order perturbation theory (CASPT2) with accurate initial condition sampling and electronic cross-section calculations.

Main Results:

• Achieved qualitative insight into excited-state dynamics and quantitative predictions of photoelectron spectra, fluorine-loss branching ratios, and translational kinetic energy release.
• Identified statistical dissociation from X̃ 2A″-B̃ 2A' states and rapid excited-state dissociation (50-250 fs) from C̃ 2A″-Ẽ 2A' states.
• CASPT2 uniquely captured excited triplet C2H3+ fragment formation, while DFT accurately predicted branching ratios.

Conclusions:

• The study successfully resolved debates on vinyl fluoride photoionization using advanced computational methods.
• Autoionizing Rydberg states are not necessary to explain experimental observations.
• SH-AIMD simulations provide a powerful tool for studying complex chemical dynamics.