|Title||ELECTRON MOMENTUM SPECTROSCOPY OF THE VALENCE ORBITALS OF ACETYLENE - QUANTITATIVE COMPARISONS USING NEAR HARTREE-FOCK LIMIT AND CORRELATED WAVE-FUNCTIONS|
|Publication Type||Journal Article|
|Year of Publication||1992|
|Authors||DUFFY, P, CLARK, SAC, Brion, CE, CASIDA, ME, Chong, DP, Davidson, ER, MAXWELL, C|
|Date Published||SEP 15|
Measurements of the complete valence shell binding energy spectrum (8-55 eV) and the corresponding orbital electron momentum distributions have been obtained using electron momentum spectroscopy. The measured momentum distributions are compared with SCF calculations using basis sets ranging from minimum basis set to very near Hartree-Fock limit in quality. The effects of relaxation and electron correlation are investigated using second-order Green's function calculations and also using configuration interaction (CI) methods. The CI calculations recover up to 66% of the estimated total parent correlation energy. In the case of acetylene all SCF calculations at the double zeta level and above give a reasonable description of the shapes of the momentum distributions and only minor differences result from inclusion of correlation and relaxation. This contrasts sharply with the situation for row two hydrides where inclusion of correlation has been found to be crucial. The calculated position and momentum density maps for the oriented C2H2 molecule are compared with the experimental results. Detailed studies of the binding energy spectrum and momentum distributions in the inner valence region demonstrate that the satellite intensity overwhelmingly arises from 2-sigma(g) ionization with only a very small satellite contribution expected from 2-sigma(u) ionization. The inner valence results are compared with earlier findings from photoelectron spectroscopy measurements and a range of theoretical calculations.