发表机构
University of Basel; National Research Council Canada; University of Ottawa（巴塞尔大学; 加拿大国家研究委员会; 渥太华大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文通过准经典轨迹模拟分析时间分辨库仑爆炸成像实验，直接观测NO2单分子衰变中的相空间演化，估计统计性时间尺度为2-3皮秒。
AI 中文摘要
对基态统计单分子衰变过程中大幅动力学的直接时间分辨观测仍是一项实验挑战。本文对一个典型的单分子反应 NO$_2$ $\rightarrow$ NO($^2\Pi, v=0, J)$ + O($^3P_j$) 在阈值解离能量下的实验时间分辨库仑爆炸成像（TR-CEI）研究（J. Chem. Phys. 151, 174301, 2019）进行了建模与分析。利用在准确且经过验证的基态势能面（PES）上进行的准经典轨迹（QCT）模拟，并结合已知产物态分布给出的能量和角动量约束，来表征解离动力学。TR-CEI 通过超快强场电离（SFI）将演化中的中性基态波包突然投影到排斥性的双电荷阳离子态上，该阳离子态随后脉冲式碎裂为 NO$^{+}$ + O$^{+}$ 离子对。在适用于较长 NO--O（雅可比）间距的库仑反冲近似下，离子对的 CEI 能量与 SFI 时刻中性基态 NO 和 O 部分之间的标量距离成反比，从而直接测量单分子衰变过程中平均 NO--O 距离的演化。QCT 模拟结果与 TR-CEI 测量结果吻合良好。本文呈现了相空间演化、回归时间分布和 Lyapunov 指数分析，支持 TR-CEI 直接观测单分子衰变过程中相空间演化的结论。对于当前体系，相空间分布达到统计性的时间尺度估计为 2 至 3 ps。
英文摘要
Direct time-resolved observation of large amplitude dynamics during ground state statistical unimolecular decay remains an experimental challenge. Here, an experimental Time-Resolved Coulomb Explosion Imaging (TR-CEI) study (J. Chem. Phys. 151, 174301, 2019) of the canonical unimolecular reaction NO$_2$ $\rightarrow$ NO($^2Π, v=0, J)$ + O($^3P_j$) at threshold dissociation energies is modeled and analyzed. Quasi-classical trajectory (QCT) simulations on an accurate and validated ground state potential energy surface (PES), with energy and angular momentum constraints from known product state distributions, are used to characterize the dissociation dynamics. TR-CEI projects suddenly, via ultrafast Strong Field Ionization (SFI), the evolving neutral ground state wavepacket onto the repulsive doubly charged cationic state which then impulsively fragments into the NO$^{+}$ + O$^{+}$ ion pair. Within the Coulomb recoil approximation, which applies at longer NO--O (Jacobi) separations, the ion pair CEI-energy is inversely proportional to the scalar distance between the neutral ground state NO and O moieties at the moment of SFI, thus providing a direct measure of the evolving average NO--O distance during unimolecular decay. Results from QCT simulations agree favourably with the TR-CEI measurements. Phase space evolution, recurrence time distributions and Lyapunov exponent analysis are presented which support the conclusion that TR-CEI directly observes phase space evolution during unimolecular decay. For the present system, the time scale for the phase space distribution to achieve statisticality is estimated to be 2 to 3 ps.
