EMS study of vibrational effects on electron momentum distributions of C₂H₄ and CH₂F₂

We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions for the outer valence orbitals of C₂H₄ and CH₂F₂. The symmetric noncoplanar (e,2e) experiment has been conducted at impact energy of 1.2 keV. Furthermore, a theoretical method of calculating electron momentum distributions has been developed with vibrational effects being involved. The experimental and theoretical results for these molecules strongly suggest that vibrational effects on electron momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.