Time delay in molecular photoionization near giant resonances

巨共振附近分子光电离的时间延迟

• 批准号: 401300715
• 负责人: Professor Dr. Matthias Kling
• 金额: --
• 依托单位: National Accelerator Laboratory SLAC
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/401300715?language=en
• 关键词: Time; delay; molecular; photoionization; near

The measurement of time delay associated with photoionization of a bound electron was enabled with attosecond metrology. Ionization time delays were predominantly evaluated both theoretically and experimentally for atoms or solids of single constituent species. Such measurements for molecules are inherently more challenging, and have just recently been reported for valence electron emission from simple triatomic molecules employing the RABBITT (attosecond beating by interference of two-photon transitions) technique. With this proposal, utilizing attosecond streaking spectroscopy we aim to study the photoionization time delay for molecules containing an iodine atom with a characteristic broadband resonance in the extreme ultraviolet, the 4d giant resonance. The resonance has been assigned to a shape resonance, which is, however, strongly affected by multi-electron, collective excitations. Recent theoretical work on the ionization time delays associated with such a resonance is highly controversial. Chakraborty and coworkers performed time-dependent density-functional-theory (DFT) simulations and predicted negative ionization time delays as a result of the collective excitation, where the shape resonance alone leads to positive delays. These results are at odds with predictions by Kheifets employing random-phase approximation (RPA) simulations. With our measurements spanning over the energy range of the iodine 4d resonance, we will be able to resolve this theoretical dispute, providing detailed insight into collective excitations in giant resonances. Furthermore, our experiments will be performed in the molecular frame detecting the molecular orientation via emitted ions with a cold-target recoil ion momentum spectrometer (COLTRIMS). The resulting data will permit to determine the ionization time delay as a function of molecular orientation as well as electron emission angle. The time delays can thus be obtained in a highly differential manner, which facilitates closer comparison to theoretical predictions. We will perform semi-classical Monte-Carlo trajectory simulations in collaboration with the Landsmann group, which incorporate the laser field influence on the time delay and can be directly compared to the experimental data. The intrinsic Eisenbud-Wigner-Smith (EWS) delay can be derived by careful consideration of the laser-field contributions. On the other hand, the EWS delay will be directly obtained from quantum mechanical scattering calculations based on the recently developed framework by the Wörner group. By comparison of the differential time delays for several molecular systems, we expect to gain detailed insight into molecular-frame photoionization on the attosecond scale.

利用阿秒计量学实现了对束缚电子光电离时间延迟的测量。电离时间延迟主要是从理论和实验两方面对单组分原子或固体进行评估。分子的这种测量本质上更具挑战性，并且最近刚刚报道了采用RABBITT（通过双光子跃迁干涉的阿秒跳动）技术的简单三原子分子的价电子发射。在这个提议下，利用阿秒条纹光谱，我们的目标是研究含有碘原子的分子的光电离时间延迟，该分子在极紫外具有特征宽带共振，即4d巨共振。的共振已被分配到一个形状的共振，这是，然而，强烈影响多电子，集体激发。最近的理论工作电离时间延迟与这样的共振是非常有争议的。Chakraborty和同事进行了时间相关密度泛函理论（DFT）模拟，并预测了集体激发的负电离时间延迟，其中形状共振单独导致正延迟。这些结果与Kheibe采用随机相位近似（RPA）模拟的预测不一致。随着我们的测量跨越碘4d共振的能量范围，我们将能够解决这一理论争议，为巨共振中的集体激发提供详细的见解。此外，我们的实验将在分子框架内进行，通过冷靶反冲离子动量谱仪（COLTRIMS）发射的离子检测分子取向。由此产生的数据将允许确定作为分子取向以及电子发射角的函数的电离时间延迟。因此，可以以高度差分的方式获得时间延迟，这有助于与理论预测进行更密切的比较。我们将与Landsmann小组合作进行半经典蒙特-卡罗轨迹模拟，其中包括激光场对时间延迟的影响，并可以直接与实验数据进行比较。本征Eisenbud-Wigner-Smith（EWS）延迟可以通过仔细考虑激光场的贡献而导出。另一方面，EWS延迟将直接从基于Wörner小组最近开发的框架的量子力学散射计算中获得。通过比较几种分子系统的微分时间延迟，我们期望获得详细的了解分子框架的光电离的阿秒尺度。