The valence orbital momentum distributions and binding energy spectra of methane by electron momentum spectroscopy: Quantitative comparisons using near Hartree-Fock limit and correlated wavefunctions

Abstract

The binding energies and electron momentum distributions of the two valence orbitals of CH 4 have been measured at high momentum resolution. The measured binding energy spectrum compares favourably with the results of previously published Green's function calculations, which predict some small splitting of the 2a 1 pole strength. At least four distinct satellite peaks (of dominantly 2a 1 symmetry) are identified in the inner valence region. The measured momentum profiles have been quantitatively compared with momentum distributions predicted using SCF wavefunctions up to near the Hartree-Fock limit in quality and also with ion-neutral overlap calculations using correlated wavefunctions obtained by the method of configuration interaction. Excellent agreement is found with theory at the Hartree-Fock limit level and inclusion of relaxation and electron correlation is found to have minimal effect on the calculated electron momentum distributions. Density maps for oriented CH 4 molecules in position and momentum space are presented.