Abstract
The non-adiabatic dynamics of furan excited in the ππ* state (S2 in the Franck–Condon geometry) was studied using non-adiabatic molecular dynamics simulations in connection with an ensemble density functional method. The time-resolved photoelectron spectra were theoretically simulated in a wide range of electron binding energies that covered the valence as well as the core electrons. The dynamics of the decay (rise) of the photoelectron signal were compared with the excited-state population dynamics. It was observed that the photoelectron signal decay parameters at certain electron binding energies displayed a good correlation with the events occurring during the excited-state dynamics. Thus, the time profile of the photoelectron intensity of the K-shell electrons of oxygen (decay constant of 34 ± 3 fs) showed a reasonable correlation with the time of passage through conical intersections with the ground state (47 ± 2 fs). The ground-state recovery constant of the photoelectron signal (121 ± 30 fs) was in good agreement with the theoretically obtained excited-state lifetime (93 ± 9 fs), as well as with the experimentally estimated recovery time constant (ca. 110 fs). Hence, it is proposed to complement the traditional TRPES observations with the trXPS (or trNEXAFS) measurements to obtain more reliable estimates of the most mechanistically important events during the excited-state dynamics.
Highlights
Time-resolved (TR) photoelectron (PE) spectroscopy (TRPES) is a pump–probe technique that is widely used to study the dynamics of photochemical reactions [1,2,3]
The SSR method is based on ensemble density functional theory, where the ground-state eDFT [37,38,39,40,41,42] is used to describe the non-dynamic electron correlation originating in multi-reference ground states of molecules and eDFT for ensembles of the ground and excited states [43,44,45,46] to obtain excitation energies from a variational time-independent computation
We investigated the dynamics of furan excited in the ππ ∗ state (S2 at the FC geometry) using non-adiabatic molecular dynamics simulations and analysis of the adiabatic potential energy surfaces and the theoretically estimated TRPE spectra
Summary
Time-resolved (TR) photoelectron (PE) spectroscopy (TRPES) is a pump–probe technique that is widely used to study the dynamics of photochemical reactions [1,2,3]. During the TRPE spectrum acquisition, a molecule is brought into an excited electronic state by the pump pulse and is subsequently probed by a series of short probe pulses, which cause ionization of the molecule and emanation of the photoelectrons [1,2,3]. The non-adiabatic relaxation to the ground state may occur through two main reaction channels: the ring-puckering channel, which involves substantial deformation of the furan ring and may result in electrocyclization, and the ring-opening channel, which results in the formation of a number of products [4,5,6,9,17,18]. TDDFT is not appropriate for non-adiabatic molecular dynamics simulations, as it fails to correctly describe the topology of conical intersections [21,22,23], the latter simulations seemed to agree with the most recent
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