PHOTOIONISATION CROSS-SECTION CALCULATIONS FOR H2O AND NH3 BY ONE-CENTER EXPANSION AND STIELTJES TECHNIQUE

Partial and total photoionisation cross sections for H2 0 and NH3 are evaluated employing a discrete basis set and using the Stieltjes imaging technique to obtain the continuum oscillator strength densities. Bound and continuum electronic eigenfunctions at the ground-state equilibrium geometry are described in the independent-channel approximation using large basis sets of integrable functions centered on the heavy atom. Besides the usual STO functions, hydrogenic Rydberg functions and diffuse oscillatory functions are used in order to improve the description of the bound excited orbitals and of'the continuum orbitals respectively. The generally good agreement with recent experimental measurements and previous theoretical works for H 20 confirms that the one-center expansion is adequate to describe photoionisation processes in molecules having the electron charge largely localized around the heavy ...