A UV-pump x-ray-probe (UVX-PP) experiment for probing UV initiated dissociation of the water molecule with long pulses is proposed on the basis of theoretical simulations. With long overlapping UV and x-ray pulses, we can obtain high-spectral-resolution x-ray-absorption or ionization spectra, containing detailed information about dynamics in the intermediate valence-excited state. The dynamics can be influenced with frequency detuning of the pump UV pulse, which acts as a camera shutter by regulating the duration of the UVX-PP process. Thereby, this UVX-PP setup gives access to ultrafast dynamics of the nuclear wave packet without experimentally challenging requirements of ultrashort pulses and controlled delay times. In a case study of the water molecule, we focus on the lowest UVX-PP channel ($1b_1\to 4a_1, 1a_1\to 1b_1$) where both intermediate valence-excited and final core-excited states are dissociative. The variation of the UVX-PP duration, controlled by the UV detuning, and different dispersion laws of so-called molecular and atomic bands allow one to study the dynamics of fragmentation of the water molecule in the intermediate state. A feature is that the long lifetime of intermediate valence-excited states opens a door for studies of photoinduced dissociation of polyatomic molecules with heavy fragments.

中文翻译：

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由长紫外脉冲诱导并由高能分辨率 X 射线吸收光谱探测的水的光解

在理论模拟的基础上，提出了一种紫外泵 X 射线探针 (UVX-PP) 实验，用于用长脉冲探测紫外引发的水分子解离。通过长重叠的紫外线和 X 射线脉冲，我们可以获得高光谱分辨率的 X 射线吸收或电离光谱，其中包含有关中间价激发态动力学的详细信息。泵浦 UV 脉冲的频率失谐可以影响动力学，它通过调节 UVX-PP 过程的持续时间充当相机快门。因此，这种 UVX-PP 设置可以访问核波包的超快动力学，而无需对超短脉冲和受控延迟时间的实验挑战要求。在水分子的案例研究中，我们关注最低的 UVX-PP 通道（$1{乙}_1\to 4{\mathrm{一种}}_1, 1{\mathrm{一种}}_1\to 1{乙}_1$) 其中中间价激发态和最终核心激发态都是解离的。由 UV 失谐控制的 UVX-PP 持续时间的变化，以及所谓的分子和原子带的不同色散规律，使人们能够研究中间状态下水分子碎裂的动力学。一个特点是中间价激发态的长寿命为研究具有重碎片的多原子分子的光致离解打开了一扇门。