Determination of outer molecular orbitals by collisional ionization experiments and comparison with Hartree-Fock, Kohn-Sham, and Dyson orbitals

Although the outer shapes of molecular orbitals (MO's) are of great importance in many phenomena, they have been difficult to be probed by experiments. Here we show that metastable helium (He-*) atoms can sensitively probe the outer properties of molecules and that an electron spectroscopic technique using velocity-selected He-* atoms in combination with classical trajectory simulations leads to a consistent determination of MO functions and the molecular surface. MO functions composed of linear combinations of atomic orbital functions were fitted to the observed collision energy dependences of partial ionization cross sections (CEDPICS). The obtained CEDPICS MO functions were compared with conventionally available Hartree-Fock, Kohn-Sham, and Dyson orbitals.