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

各种分子性质如反应性是由特定价电子的分子轨道模式决定的。本项目的目的是开发一种在动量空间中对这种分子轨道模式进行成像的方法。为了实现这个项目，我们建造了一个装置，旨在检测两个出射电子和电子康普顿散射产生的碎片离子的三重重合，并测量三个带电粒子之间的矢量相关性。该装置随后被用于H_2和O_2分子的解离电离过程。实验结果虽然存在较大的统计不确定性，但符合我们的预期。例如，H_2分子的2_<Sδ_g>电子轨道在动量空间中被观察到沿垂直于分子轴的方向被拉长，而在位置空间中则是沿分子轴被拉长。这个结论完全是由傅里叶变换的性质决定的。另一方面，对于分子的2_<Pδ_u>轨道，清晰地观察到其波瓣和节面分别位于平行于分子轴方向和垂直于分子轴方向的p型轨道性质。通过这种方式，我们第一次成功地证明了以三维形式观察分子轨道是完全可能的。该项目的成果被高度评价为分子轨道成像的开创性工作，为分子束缚电子波函数的详细研究打开了大门。这项工作已被邀请参加广泛的国际和国内会议（40次邀请演讲），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.