Binary (e, 2e) spectroscopic study and momentum space chemistry of the two-electron systems He and H 2

Abstract

The spherically averaged momentum distributions of the ground-state orbitals of the two-electron systems He(1s) and H 2(1σ g) have been determined using an improved high momentum resolution (Δ p ≈ 0.1 a o −1 fwhm) binary (e, 2e) spectromet The present result for He(1s) is in excellent agreement with the earlier (e, 2e) measurements. Similarly the result for H 2(1σ g) is in good agreement with earlier (e, 2e) measurements by Weigold et al. and Dey et al. However, for H 2 the recent measurement reported by Midgall et al. is not in agreement with the present or earlier work. The results are compared with theoretical momentum distributions calculated using wavefunctions of varying quality ranging from minimal basis to extended Hartree-Fock. In addition the binary (e, 2e) momentum distributions measured in the present work for the two-electron systems He and H 2 are found to be in good agreement with those derived from the experimental Compton profiles reported by Lee. Momentum density and density difference maps are used in comparison with their respective position-space counterparts to provide a complementary perspective to chemical binding phenomena and to further extend the study and understanding of momentum-space chemical properties. This alternative topographical view of chemical binding and bond formation is discussed in detail for the process H+H → H 2(1σ g) as a function of internuclear separation.