Mapping the photochemistry of cyclopentadiene: from theory to ultrafast X-ray scattering

Abstract

The photoinduced ring-conversion reaction when cyclopentadiene (CP) is excited at 5.10 eV is simulated using surface-hopping semiclassical trajectories with XMS(3)-CASPT2(4,4)/cc-pVDZ electronic structure theory. In addition, PBE0/def2-SV(P) is employed for ground...

The Ring-Closing Reaction of Cyclopentadiene Probed with Ultrafast X-ray Scattering

“…At longer delay times, extending into the picosecond range, notable intensity changes are observed in the difference signal in the q = 4–5 Å range, accompanied by an increase in intensity in the region around q = 1.5–2 Å. This behavior, specifically the decrease in intensity in the higher q region, is indicative of the thermal backreaction from vibrationally hot BP to the vibrationally hot ground state CP hot and is consistent with the theoretical model . This eventually results in an equilibrium between BP and CP hot , which is reasonable considering that the energy barrier for the thermal backreaction from BP to CP hot requires 1.13 eV and the reverse reaction 3.21 eV. , These values are lower than the energy supplied into the system following excitation with a 5.10 eV photon.…”

“…The fits provide the kinetic time constants listed in Table . The initial reaction of CP* to BP is very fast, with a time constant of 88 ± 10 fs, which is in excellent agreement with previous theoretical work. , The time constants for creation of CP hot and RO are much slower, but it should be understood that the branching into different reaction products occurs on the excited-state surface and reflects the ultrafast evolution of the wave packet. The slower kinetic time constants arise from the modeling of the dynamic reaction using a kinetics scheme.…”

“…In an extension of Kuhlman's work, Bertram et al simulated nonadiabatic transitions using surface-hopping trajectories to further investigate the excited-state dynamics of CP, specifically focusing on the electrocyclization into BP. 27 In these simulations, the formation of BP was monitored by the C 1 −C 4 bond distance and the C 1 −C 5 −C 4 bond angle (as labeled in Scheme 1), both of which significantly decrease (from 2.36 to 1.54 Å for the bond distance and from 103.4 to 60.7°for the bond angle). 27 While these theoretical advances are intriguing, experimental evidence for the ring-closing reaction into BP remains wanting.…”

“…27 In these simulations, the formation of BP was monitored by the C 1 −C 4 bond distance and the C 1 −C 5 −C 4 bond angle (as labeled in Scheme 1), both of which significantly decrease (from 2.36 to 1.54 Å for the bond distance and from 103.4 to 60.7°for the bond angle). 27 While these theoretical advances are intriguing, experimental evidence for the ring-closing reaction into BP remains wanting. In search of experimental verification of BP formation, we investigate the time-resolved structural relaxation dynamics of CP excited at 243 nm with ultrafast gas-phase X-ray scattering.…”

Extracting the electronic structure signal from X-ray and electron scattering in the gas phase

“…Time-resolved experiments can thus detect the rearrangement of electrons due to photoexcitation (Yong et al, 2020), changes in inelastic scattering due to changes in electronic state populations (Yang et al, 2020), dynamic charge transfer (Yong et al, 2021b), the breaking of chemical bonds (Ruddock et al, 2019), or carry out tomography on rotational wave packets (Zhang et al, 2021). Interesting future directions for scattering experiments are also actively explored via simulations (Mu et al, 2023;Bertram et al, 2023). Given sufficient time-resolution, it should become possible to track the dynamics of electrons in a molecular system (Simmermacher et al, 2019a,b;Ziems et al, 2023).…”