VALENCE ELECTRON MOMENTUM DISTRIBUTIONS OF THE HYDROGEN HALIDES .1. COMPARISON OF EMS MEASUREMENTS AND CALCULATIONS USING HARTREE-FOCK LIMIT AND CONFIGURATION-INTERACTION WAVE-FUNCTIONS FOR HYDROGEN-FLUORIDE

The valence orbital momentum profiles of hydrogen fluoride have been obtained using electron momentum spectroscopy at an impact energy of 1200 eV. The present results show significant differences from earlier measurements (J. Electron Spectry. Relat. Phenom. 21 (1980) 71) for the (3sigma)-1 ionization but are in good agreement for the (1pi)-1 and (2sigma)-1 processes. The measurements are compared with calculations ranging from minimum basis set to highly saturated basis sets essentially at the Hartree-Fock limit and also with numerical Hartree-Fock calculations. The experimental momentum resolution is incorporated into the calculations using the recently developed GW-PG resolution folding method (Chem. Phys. 159 (1992) 347). The significant discrepancy remaining between SCF limit calculations and experiment indicates the importance of electron correlation and relaxation effects in describing the momentum profile corresponding to the removal of the 1pi electron. These effects are investigated using multireference singles and doubles CI calculations of the full ion-neutral overlap distribution and considerable improvement in the agreement between theory and experiment is then achieved.