Development of a method for imaging molecular orbital pattern and foundation of momentum spectroscopy

特定价电子的分子轨道模式决定了分子的各种性质，如反应性等。本项目的目的是开发一种在动量空间中成像这种分子轨道模式的方法。为了实现本项目，我们已经建立了一个装置，旨在检测三重符合的两个出射电子和电子康普顿散射产生的碎片离子，并测量三个带电粒子之间的矢量相关性。该装置已用于H_2和O_2分子的离解电离过程。虽然实验结果遭受相当大的统计不确定性，他们被发现满足我们的期望。例如，H_2分子的2_<Sδ_g>电子轨道在动量空间中被观察到在垂直于分子轴的方向上被拉长，而在位置空间中被沿着分子轴拉伸。这种观察完全是由于傅里叶变换的性质。另一方面，对于2_<Pδ_u>轨道，则清楚地观察到了p型轨道的性质，即波瓣和节面分别位于平行和垂直于分子轴的方向上。这一成果被认为是分子轨道成像的开创性工作，为深入研究分子的束缚电子波函数打开了大门。这项工作已被邀请参加广泛的国际和国内会议（40个特邀演讲），并于2008年3月向首席研究员提供了日本化学学会（CSJ）创造性工作奖。

Various kinds of molecular properties such as reactivity are governed by molecular orbital pattern of a specific valence electron. The purpose of this project is to develop a method for imaging such molecular orbital pattern in momentum space.In order to realize this project, we have constructed an apparatus that aims to detect in triple coincidence the two outgoing electrons and the fragment ion produced by electron Compton scattering and to measure vector correlations among the three charged particles. The apparatus has been subsequently employed for dissociative ionization processes of the H_2 and O_2 molecules. Although the experimental results suffer from rather large statistical uncertainties, they are found to fulfill our expectations. For instance, the 2_<Sδ_g> electron orbital of the H_2 molecule has been observed in momentum space as what is elongated in the direction perpendicular to the molecular axis, which is well known to be stretched along the molecular axis in position space. This observation is due entirely to nature of Fourier transform. On the other hand, for the 2_<Pδ_u> orbital of the molecule, the p-type orbital nature, which lobes and a nodal plane lie in the direction parallel and perpendicular to the molecular axis respectively, has been clearly observed. In this way, we have successfully demonstrated for the first time that looking at molecular orbitals in the three dimensional form is totally possible.The achievements of this project has been highly evaluated as pioneering work for molecular orbital imaging, opening the door for detailed studies on bound electronic wave functions of molecules. This work has been invited to a broad range of international and domestic conferences (40 invited talks) and The Chemical Society of Japan (CSJ) Award for Creative Work has been provided to the head investigator in 2008 March.