Ultrafast Dissociation Dynamics of Inner-Shell Excited Molecules

按照提出的计划，我们在本项目中进行了如下三种实验，特别强调了第二和第三种实验，目的是直接观察一些简单分子在核孔态下的超快核运动：(1)利用圆柱形镜像电子能量分析仪测量高分辨率共振奥歇电子能谱；(2)测量未解析共振峰内CO_2激发的所有碎片的波长相关不对称参数（β值）；(3)直接测量谐振内壳激发后产生的所有碎片离子的线性动量分布。最后一个主题包括开发一种新技术，该技术包括使用带有延迟线阳极的位置敏感二维探测器进行飞行时间测量。在许多成功的结果中，最突出的是对两个雷纳-泰勒分裂态的单独观察，这是由上述线性动量分布测量实现的。C1s^<-1>2π_υ和O1s^<-1>2π_υ的核孔态通过与弯曲振动的振动耦合预测为两个能级：一个是π轨道位于弯曲平面（弯曲结构），另一个是π轨道从弯曲平面垂直挤出（线性结构），但这两个能级从未单独观察过。利用目前的技术，我们可以利用对应于两个O^+碎片离子的两个动量的矢量积，很好地观察到这些能级中的一个能级与另一个能级分开。这样就清楚地表明，解离前的分子在前一能级的激发下比在后一能级的激发下弯曲得更大。这被解释为反映了核在核心激发态向平衡几何方向的运动。这代表了C1s^<-1>2π_υ和O1s^<-1>2π_υ核孔态（Renner-Teller分裂对）的线性和弯曲结构的首次直接验证。少

Following the proposed plan, we have performed in the present project three types of experiments shown below, placing particular emphasis on the second and third experiments which aim at direct observation of ultrafast nuclear motion in the core-hole state of some simple molecules : (1) measurements of high resolution resonance Auger electron spectra with a cylindrical mirror electron energy analyzer, (2) measurements of wavelength-dependent asymmetry parameter (βvalues) for all fragments from the inner-shell excited CO_2 within an unresolved resonance peak, (3) direct measurements of linear momentum distribution of all fragment ions produced following resonant inner-shell excitation. The last subject included development of a new technique consisting of a time-of-flight measurement using a position-sensitive two-dimensional detectors with delay-line anodes.The most prominent among many successful results is the separate observation of the two Renner-Teller split states as achieved by … More the above-mentioned linear momentum distribution measurements. Each of the C1s^<-1>2π_υ and O1s^<-1>2π_υ core-hole states is predicted to be split into two levels by the vibronic coupling with the bending vibration : one is which the π orbital lies in the bending plane (bent structure) and the other in which it extrudes perpendicularly from the bending plane (linear structure), but these levels have never been observed separately. With the present technique, we could nicely observe one of these levels separately from the other by utilizing vector products of the two momenta corresponding to the two O^+ fragment ions. In this way it has clearly been shown that the molecules just before the dissociation are more bent with the excitation to the former level than with that to the latter level. This is interpreted as reflecting the nuclear motion in the core-excited states towards the equilibrium geometry. This represents the first direct verification of the occurrence of linear and bent structures for the C1s^<-1>2π_υ and O1s^<-1>2π_υ core-hole state (Renner-Teller split pair). Less