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Abstract
Mechanistic insights into photodissociation dynamics of transition metal carbonyls, like Fe(CO)$_5$, are fundamental for understanding active catalytic intermediates. Although extensively studied, the ultrafast structural dynamics of these systems remain elusive. Using ultrafast X-ray scattering, we uncover the ultrafast photochemistry of Fe(CO)$_5$ in real space and time, observing synchronous oscillations in atomic pair distances, followed by a prompt rotating CO release preferentially in the axial direction. This behavior aligns with simulations, reflecting the interplay between the axial Fe-C distances' potential energy landscape and non-adiabatic transitions between metal-to-ligand charge-transfer states. Additionally, we characterize a secondary delayed CO release associated with a reduction of Fe-C steady state distances and structural dynamics of the formed Fe(CO)$_4$. Our results quantify energy redistribution across vibration, rotation, and translation degrees of freedom, offering an ultrafast microscopic view of complex structural dynamics, enhancing our grasp on Fe(CO)$_5$ photodissociation and advancing our understanding of transition metal catalytic systems.
Supplementary materials
Title
Supplementary Discussions: Real-space Observation of a Transition Metal Complex Dissociation and Energy Redistribution
Description
This document provides a comprehensive analysis of molecular dynamics, focusing on scattering data collection, pair density dynamics, and extrapolation techniques. It begins with the collection and initial scattering analysis, followed by the extrapolation of simulated pair density dynamics, addressing both dissociative and non-dissociative pairs, and estimating the associated errors. The simulation of scattering from trajectories is discussed alongside real-space inversion of scattering signals. The kinetic model for CO dissociation, estimation of dissociation velocity, rotation frequency, and energy partition analysis are explored. Additionally, the document delves into normal mode analysis for Fe(CO)₄ across different electronic states, determining mode contributions to experimental observations. It also estimates the experimental instrument response function, examines laser pulse energy scans, and includes supplementary figures for additional context.
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