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

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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.