The ultrafast electronic decay of HCl molecules in the time domain after resonant core excitation was measured. Here, a Cl-2p core electron was promoted to the antibonding σ* orbital initiating molecular dissociation, and simultaneously, the electronic excitation relaxes via an Auger decay. For HCl, both processes compete on similar ultrashort femtosecond time scales. In order to measure the lifetime of the core hole excitation, we collinearly superimposed 40 fs soft x-ray pulses with intense terahertz (THz) radiation from the free-electron laser in Hamburg (FLASH). Electrons emitted from the molecules are accelerated (streaked) by the THz electric field where the resulting momentum change depends on the field's phase at the instant of ionization. Evaluation of a time-shift between the delay-dependent streaking spectra of photo- and Auger electrons yields a decay constant of (11 ± 2) fs for LMM Auger electrons. For further validation, the method was also applied to the MNN Auger decay of krypton. Reproduction of the value already published in the literature confirms that a temporal resolution much below the duration of the exciting x-ray pulses can be reached.

中文翻译：

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通过THz条纹探测核心激发的HCl分子的电子衰减。

测量了共振核激发后时域中HCl分子的超快电子衰减。在此，Cl-2p核心电子被促进到反键σ*轨道引发的分子解离，同时，电子激发通过俄歇衰变而松弛。对于HCl，这两个过程在相似的超短飞秒时间尺度上竞争。为了测量核心孔激发的寿命，我们将来自汉堡的自由电子激光器（FLASH）的40 fs软X射线脉冲与强烈的太赫兹（THz）辐射共线叠加。从分子发出的电子被太赫兹电场加速（斑纹），其中产生的动量变化取决于电离瞬间电场的相位。对光电子和俄歇电子的依赖于延迟的条纹光谱之间的时移进行评估，得出LMM俄歇电子的衰减常数为（11±2）fs。为了进一步验证，该方法还应用于the的MNN Auger衰减。再现已经在文献中发表的值证实了可以达到远低于激发X射线脉冲持续时间的时间分辨率。