Predicting the photodynamics of cyclobutanone triggered by a laser pulse at 200 nm and its MeV-UED signals -- a trajectory surface hopping and XMS-CASPT2 perspective

Abstract

This work is part of a prediction challenge that invited theoretical/computational chemists to predict the photochemistry of cyclobutanone in the gas phase, excited at 200 nm by a laser pulse, and the expected signal that will be recorded during a time-resolved megaelectronvolt ultrafast electron diffraction (MeV-UED). We present here our theoretical predictions based on a combination of trajectory surface hopping with XMS-CASPT2 (for the nonadiabatic molecular dynamics) and Born-Oppenheimer molecular dynamics (BOMD) with MP2 (for the athermal ground-state dynamics following internal conversion), coined (NA+BO)MD. The initial conditions were sampled from BOMD coupled to a quantum thermostat. Our simulations indicate that the main photoproducts after 2 ps of dynamics are CO + cyclopropane (50%), CO + propene (10%), and ethene and ketene (34%). The photoexcited cyclobutanone in its second excited electronic state S${}_2$ can follow two pathways for its nonradiative decay: (i) a ring-opening in S${}_2$ and a subsequent rapid decay to the ground electronic state, where the photoproducts are formed, or (ii) a transfer through a closed-ring conical intersection to S${}_1$, where cyclobutanone ring opens and then funnels to the ground state. Lifetimes for the photoproduct and electronic populations were determined. We calculated a stationary MeV-UED signal [difference pair distribution function - $\Delta$PDF$(r)$] for each (interpolated) pathway as well as a time-resolved signal [$\Delta$PDF$(r,t)$ and $\Delta I/I(s,t)$] for the full swarm of (NA+BO)MD trajectories. Furthermore, our analysis provides time-independent basis functions that can be used to fit the time-dependent experimental UED signals and potentially recover the population of photoproducts. We also offer a detailed analysis of the limitations of our model and their potential impact on the predicted experimental signals.

References in corpus (7)

• Nuclear quantum effects in solids using a colored-noise thermostat
• Colored-noise thermostats à la carte
• BAGEL: Brilliantly Advanced General Electronic-structure Library
• eT 1.0: an open source electronic structure program with emphasis on coupled cluster and multilevel methods
• Deciphering the Influence of Ground-State Distributions on the Calculation of Photolysis Observables
• Monitoring the evolution of relative product populations at early times during a photochemical reaction
• Predicting the photodynamics of cyclobutanone triggered by a laser pulse at 200 nm and its MeV-UED signals -- a trajectory surface hopping and XMS-CASPT2 perspective

Cited by in corpus (4)

• Predicting the photodynamics of cyclobutanone triggered by a laser pulse at 200 nm and its MeV-UED signals -- a trajectory surface hopping and XMS-CASPT2 perspective
• Imaging the photochemical dynamics of cyclobutanone with MeV ultrafast electron diffraction
• Simulating Ultrafast Transient Absorption Spectra from First Principles using a Time-Dependent Configuration Interaction Probe
• Generalized quantum master equations can improve the accuracy of semiclassical predictions of multitime correlation functions