Experimental determination of ground-state correlation effects in molecular nitrogen

High-energy (25--28-keV) electron-impact spectroscopy (HEEIS) has been used to measure a relatively complete Bethe surface for molecular nitrogen. This surface, placed on an absolute scale by Bethe-sum-rule normalization of the generalized oscillator strength (GOS), has been employed to obtain the x-ray incoherent scattering factor S(K) as a function of the momentum transfer K by use of a sum rule of the GOS. Ground-state correlation effects on S(K) were obtained by comparing the experimental results with theory based on a near-Hartree-Fock molecular wave function. The results are compared with recent theoretical calculations of valence-shell correlation effects. It is argued that x-ray and electron-scattering experiments offer the most sensitive tests currently available for valence-shell electron-correlation effects in the ground electronic states of molecules. The results obtained coupled with available theory suggest that correlation effects on the one-electron density play a dominant role in the determination of the total correlation energy of the nitrogen molecule.