Time Resolved Photoelectron Spectroscopy as a Test of Electronic Structure and Nonadiabatic Dynamics

Abstract

We compare different levels of theory for simulating excited state molecular dynamics and use time-resolved photoelectron spectroscopy measurements to benchmark the theory. We perform trajectory surface hopping simulations for uracil excited to the first bright state (ππ*) using three different levels of theory (CASSCF, MRCIS, and XMS-CASPT2) in order to understand the role of dynamical correlation in determining the excited state dynamics, with a focus on the coupling between different electronic states and internal conversion back to the ground state. These dynamics calculations are used to simulate the time-resolved photoelectron spectra. The comparison of the calculated and measured spectra allows us to draw conclusions regarding the relative insights and quantitative accuracy of the calculations at the three different levels of theory, demonstrating that detailed quantitative comparisons of time-resolved photoelectron spectra can be used to benchmark methodology.

Nonadiabatic Excited State Dynamics of Organic Chromophores: Take-Home Messages

“…The NewtonX package is used for the TSH calculations , coupled with the electronic structure packages Columbus , or Bagel . Details on the specifics can be found in the original publications. − …”

“…The pump and probe beams propagate parallel through the lens and perpendicular to the molecular beam. At the end of the VMI spectrometer, there is a position-sensitive 2D detector, consisting of two microchannel-plates (MCPs) in Chevron configuration together with a phosphor screen. , …”

Electronic coherences in nonadiabatic molecular photophysics revealed by time-resolved photoelectron spectroscopy

“…Recent advances employ XUV ( 27 , 28 ) and X-ray pulses ( 29 , 30 ). In these experiments, the signal provides access to the populations of the molecular states, and most theoretical methods interpret photoelectron spectra in terms of a semiclassical Fermi’s golden rule, where the role of molecular coherences is entirely neglected ( 31 – 33 ).…”

“…For comparison, we note that the time-resolved photoelectron signal is most commonly simulated using a semiclassical expression based on Fermi’s golden rule ( 31 – 33 ), where is the Fourier transform of the pulse envelope and …”

“…Alternatively, molecules with more localized nuclear wave packets passing through the CoIn would exhibit a larger and longer-lived coherence and would thus enhance the coherence signature in the TRPES signal. The standard semiclassical approaches typically used to predict photoelectron spectroscopy signals ( 31 – 33 ) do not account for molecular coherences and thus miss these experimentally accessible signatures.…”