Janoš Jiří, Figueira Nunes Joao Pedro, Hollas Daniel, Slavíček Petr, Curchod Basile F E
Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6 166 28, Czech Republic.
Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.
J Chem Phys. 2024 Apr 14;160(14). doi: 10.1063/5.0203105.
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 with MP2 (for the athermal ground-state dynamics following internal conversion), coined (NA+BO)MD. The initial conditions were sampled from Born-Oppenheimer molecular dynamics 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 S2 can follow two pathways for its nonradiative decay: (i) a ring-opening in S2 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 S1, 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-ΔPDF(r)] for each (interpolated) pathway as well as a time-resolved signal [ΔPDF(r,t) and ΔI/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 [both ΔPDF(r,t) and ΔI/I(s,t)] 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.
这项工作是一项预测挑战的一部分，该挑战邀请理论/计算化学家预测环丁酮在气相中的光化学过程，用激光脉冲在200 nm激发，以及在时间分辨兆电子伏特超快电子衍射（MeV-UED）过程中记录的预期信号。我们在此展示基于轨迹表面跳跃与XMS-CASPT2（用于非绝热分子动力学）以及玻恩-奥本海默分子动力学与MP2（用于内转换后的无热基态动力学）相结合的理论预测，简称为（NA+BO）MD。初始条件是从与量子恒温器耦合的玻恩-奥本海默分子动力学中采样得到的。我们的模拟表明，动力学2 ps后的主要光产物是CO + 环丙烷（50%）、CO + 丙烯（10%）以及乙烯和乙烯酮（34%）。处于第二激发电子态S2的光激发环丁酮的非辐射衰变可以遵循两条途径：（i）在S2中开环并随后快速衰变到基电子态，在此形成光产物，或者（ii）通过闭环锥形交叉点转移到S1，在S1中环丁酮环打开然后汇聚到基态。确定了光产物的寿命和电子布居。我们为每条（插值）途径计算了一个静态的MeV-UED信号[差分对分布函数-ΔPDF(r)]以及（NA+BO）MD轨迹的整个群体的时间分辨信号[ΔPDF(r,t)和ΔI/I(s,t)]。此外，我们的分析提供了与时间无关的基函数，可用于拟合随时间变化的实验UED信号[ΔPDF(r,t)和ΔI/I(s,t)]，并有可能恢复光产物的布居。我们还详细分析了我们模型的局限性及其对预测实验信号的潜在影响。
