Influence of molecular vibrations on the valence electron momentum distributions of adamantane

We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions of the outer valence orbitals of adamantane (C10H16). The symmetric noncoplanar (e, 2e) experiment has been carried out at an incident electron energy of 1.2 keV. Furthermore, theoretical calculations of the electron momentum distributions with vibrational effects being involved have been performed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of the complex nature of the vibrational structure of this large molecule, both approaches provide overall quantitative insights into the results of the experiment. Comparisons between experiment and theory have shown that ground state nuclear dynamics appreciably affects the momentum profiles of the 7t(2,) {2t(1) + 3e}, and {5t(2) + 5a(1)} orbitals. It has been demonstrated that changes in the momentum profiles are mainly due to the vibrational motions associated with the CH bonds. Published by AIP Publishing.