Electron momentum spectroscopy of cyclopropane

Abstract

The complete valence shell electron separation energy spectra and momentum distributions are measured for cyclopropane (C3H6) by high momentum resolution electron momentum spectroscopy (EMS) at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green function methods are carried out and compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane wave impulse approximation (PWIA) formalism using the double zeta quality molecular wavefunction of Snyder and Basch (1972). The agreement between the measured momentum distributions and the PWIA-SCF orbital momentum distributions is, in general, fair, although for the outer valence 2e' and 1e" states the SCF wavefunction underestimates the density at low momentum. The inner valence 1e' and 1a1' orbitals are found to be split by final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is quite good, although the measured separation energy spectra contain significant strength up to 40 eV, this strength being of 1e' and 1a1' origin. The controversy with respect to the assignment of the 1a2" and 2a1' valence orbitals is examined in detail with the present EMS results and third-order algebraic diagrammatic construction ADC(3) Green function calculations seemingly leading to a diametrically opposite conclusion.