Simulating Nonadiabatic Dynamics in Benzophenone: Tracing Internal Conversion Through Photoelectron Spectra

TL;DR

This study uses advanced simulations and spectroscopy to explore the internal conversion processes in benzophenone, revealing how conical intersections influence excited state populations and photoelectron signals.

Contribution

It provides new insights into the internal conversion mechanisms within benzophenone's singlet states, especially the role of conical intersections, using combined quantum dynamics and spectroscopic methods.

Findings

Nonadiabatic relaxation via conical intersections increases singlet excited state population.

Photoelectron bifurcation directly indicates population transfer.

Clarifies the role of the degenerate third singlet state.

Abstract

Benzophenone serves as a prototype chromophore for studying the photochemistry of aromatic ketones, with applications ranging from biochemistry to organic light-emitting diodes. In particular, its intersystem crossing from the first singlet excited state to triplet states has been extensively studied, but experimental or theoretical studies on the preceding internal conversion within the singlet manifold are very rare. This relaxation mechanism is particularly important because direct population transfer of the first singlet excited state from the ground state is inefficient due to its low oscillator strength. In this work, we aim to fill this gap by employing mixed quantum classical and full quantum dynamics simulations and time-resolved photoelectron spectroscopy for gas-phase benzophenone and meta-methyl benzophenone. Our results show that nonadiabatic relaxation via conical intersections leads to a linear increase in the population of the first singlet excited state. This population transfer due to conical intersections can be directly detected by a bifurcation of the photoelectron signal. In addition, we are able to clarify the role of the third singlet excited state degenerate to the second excited state - a topic that remains largely unexplored in the existing literature on benzophenone.