Rendler Nicolas, Scognamiglio Audrey, Barranco Manuel, Pí Marti, Halberstadt Nadine, Dulitz Katrin, Stienkemeier Frank
Institute of Physics, University of Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany.
Laboratoire des Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, CNRS UMR 5589, 118 route de Narbonne, 31062 Toulouse Cedex 09, France.
J Phys Chem A. 2021 Oct 21;125(41):9048-9059. doi: 10.1021/acs.jpca.1c05467. Epub 2021 Oct 7.
We present an experimental study of the dynamics following the photoexcitation and subsequent photoionization of single Cs atoms on the surface of helium nanodroplets. The dynamics of excited Cs atom desorption and readsorption as well as CsHe exciplex formation are measured by using femtosecond pump-probe velocity map imaging spectroscopy and ion time-of-flight spectrometry. The time scales for the desorption of excited Cs atoms off helium nanodroplets as well as the time scales for CsHe exciplex formation are experimentally determined for the 6p states of Cs. For the 6p Π state, our results confirm that the excited Cs atoms only desorb from the nanodroplet when the excitation wavenumber is blue-shifted from the 6p Π ← 6s Σ resonance. Our results suggest that the dynamics following excitation to the 6p Π state can be described by an evaporation-like desorption mechanism, whereas the dynamics arising from excitation to the 6p Σ state is indicative for a more impulsive desorption process. Furthermore, our results suggest a helium-induced spin-orbit relaxation from the 6p Σ state to the 6p Π state. Our findings largely agree with the results of time-dependent He density functional theory (DFT) simulations published earlier [ , , 94].
我们展示了一项关于氦纳米液滴表面单个铯原子光激发及随后光电离后动力学的实验研究。通过使用飞秒泵浦 - 探测速度映射成像光谱和离子飞行时间光谱法，测量了激发态铯原子的解吸和再吸附动力学以及铯氦激基复合物的形成。针对铯的6p态，通过实验确定了激发态铯原子从氦纳米液滴上解吸的时间尺度以及铯氦激基复合物形成的时间尺度。对于6p Π态，我们的结果证实，只有当激发波数从6p Π ← 6s Σ共振发生蓝移时，激发态铯原子才会从纳米液滴上解吸。我们的结果表明，激发到6p Π态后的动力学可以用类似蒸发的解吸机制来描述，而激发到6p Σ态产生的动力学则表明是一个更具脉冲性的解吸过程。此外，我们的结果表明存在氦诱导的从6p Σ态到6p Π态的自旋 - 轨道弛豫。我们的发现与早期发表的含时氦密度泛函理论（DFT）模拟结果[,, 94]在很大程度上一致。
