Control of photodissociation reaction of fluoromethane molecules using deformation in core-excited state

首先，设计并构建了一台配备二维位置灵敏检测器的Wiley-McLarlen型飞行时间质谱仪，该检测器由延迟线型阳极和微通道板组成。将该装置沿水平方向安装到真空室中。该室安装在广岛大学的希索的软X射线束线BL 6的终端站。同步辐射被高分辨率单色器分散并引入腔室。用氮气分子（N_2）对装置的性能进行了测试。N_2的Is电子光激发后产生碎片离子（N^+，N^<++>），用二维探测器探测。碎片离子在检测器上的观察图像显示出同心形状。在轴向反冲近似下，核激发线性分子的光解离速率远快于分子的旋转速率。其次，通过测量飞行时间谱和探测器上的位置像，得到了N^+和N^<++>在N1s->σ^* 共振激发后的动量像。所得到的解离碎片离子的初始动量矢量由于π → π跃迁而强烈地向入射光的电矢量方向分布。最后，研究了CHF_3分子核激发态在C K边的衰变动力学。随着激发能的增加，H^+的动能分布峰向高能侧移动。在C1 s-> 3 p共振激发下，（H^+-F^+）和（H^+-C^+）体系中H^+的动能分布比（H^+-CF ^+）和（H^+-CF^+）体系中的动能分布向高能侧移动。

At first, a Wiley-McLarlen type time-of-flight (TOF) mass spectrometer equipped with a two-dimensional position-sensitive detector, which was composed of a delay-line-type anode and Microchannel plates, was designed and constructed. The apparatus was installed into a vacuum chamber in the horizontal direction. The chamber was mounted as an endstation of the soft x-ray beamline BL6 of HiSOR in Hiroshima University. Synchrotron radiation was dispersed by a high-resolution monochromator and introduced into the chamber. Performance of the apparatus was tested using nitrogen molecule (N_2). Fragment ions (N^+, N^<++>) were produced after a photoexcitation of the nitrogen Is electron of N_2 and detected by the two-dimensional detector. The observed image for the fragment ions on the detector shows a concentric shape. This is quite reasonable based on the axial-recoil approximation in photodissociation of core-excited linear molecules, in which dissociation is much faster than molecular rotation.Next, the momentum images of N^+ and N^<++> were obtained after the N1s->σ^* resonant excitation by measuring the TOF spectra and position images on the detector. The obtained initial momentum vector of the fragment ion in dissociation is strongly distributed toward the direction of the electric vector of the incident light due to the Σ->Σ transition. Thus, the performance of the apparatus was satisfied sufficiently.Finally, the decay dynamics of core-excited CHF_3 molecule was investigated in the C K-edge. The peak of the kinetic-energy distribution of H^+ moves to high-energy side with the increase in excitation energy. At the C1s->3p resonant excitation, the kinetic-energy distributions of H^+ for (H^+-F^+) and (H^+-C^+) move to high-energy side in comparison with those for (H^+-CF_2^+) and (H^+-CF^+).