Violation of the adiabatic approximation observed in vibrational structures of a molecular ion at the photoionization

为了研究分子框架中的k壳层光电子角分布（PAD），我们在SPring-8上利用单色波动辐射研制了一种高动量分辨率的多电子-离子符合动量成像装置。该装置由电子和离子飞行时间谱仪、多击二维位置敏感探测器、超声速样品射流和快速TDC系统组成，该系统由12位/100 MHz晶体振荡器计数器和7个时间-幅度转换器组成，最多可接收6个启动脉冲和1个停止信号。在40 μs的时间干扰下，该TDC的时间分辨率约为120ps。利用该仪器测量了分子框架中分子的振动分辨光电子角分布，并在O 1s→5σ_g^*形状共振区明确了CO_2的振动分辨O 1s pad。利用偏松弛的Hartree-Fock近似与理论计算结果进行了比较，阐明了部分波分量在光电子发射的反对称伸缩振动模式信号中的作用。然后，我们测量了N 1s→σ^*形状共振区域中NO的振动和多倍分辨N 1s pad。NO的n1s电离区在413 eV和415 eV附近存在两个极大值，这两个极大值可以解释为σ^*形状共振、振荡、脱落或交换分裂。比较两个极大值附近的pad是非常有趣的，这为小分子k壳层的电子发射机制提供了丰富的信息。此外，该装置还用于澄清CO_2，C_2H_2和NO_2等小分子在k壳激发和/或电离后离子分解前的分子变形。综上所述，我们开发了多符合动量成像装置，用于获得分子框架中具有振动分辨率的光电子角分布，并阐明了小分子k壳层电子中光电子发射过程的详细机制。少

We have developed a multiple electron-ion-coincidence momentum imaging apparatus with high momentum resolution using monochromatized undulator radiation at SPring-8, in order to study K-shell photoelectron angular distribution(PAD) in the molecular frame. This apparatus consists of electron and ion time-of-flight spectrometers with multi-hit two-dimensional position sensitive detectors, a supersonic jet of samples, and a fast TDC system, which is composed of 12 bits/100 MHz crystal oscillator counters and 7 time-to-amplitude converters and can receive signals up to 6 as start pulses and one signal as a stop signal. The time resolution of this TDC is about 120 ps under the time spam of 40 μs. Using this apparatus we have measured vibration-resolved photoelectron angular distributions of molecules in the molecular frame and clarified the vibration-resolved O 1s PADs from CO_2 in the O 1s→5σ_g^* shape resonance region. The PADs are compared with the theoretical calculation using a partial … More ly relaxed Hartree-Fock approximation, which elucidated a role of partial wave components in the anti-symmetric-stretching vibrational mode signals for photoelectron emission. Then, we have measured vibration- and multiplet-resolved N 1s PADs from NO in the N 1s→σ^* shape resonance region. There are two maxima in the N 1s ionization region of NO, around 413 and 415 eV, which were interpreted as σ^* shape resonance, shake up, shake off, or exchange splitting. It has been found very interesting to compare the PADs around the two maxima each other, which are giving fruitful information on electron emission mechanisms from the K-shell of small molecules. Further this apparatus has served for clarification of molecular deformation just before ionic decomposition following K-shell excitation and/or ionization in small molecules like CO_2,C_2H_2 and NO_2.In conclusion, we have developed the multi-coincidence momentum imaging apparatus for obtaining the photoelectron angular distributions with vibrational resolution in the molecular frame and clarified detailed mechanisms of photoelectron emission processes in the K-shell electrons of small molecules. Less