APPLICATION OF THE (Z-CORE ANALOGY MODEL TO TETRAHEDRAL COMPOUNDS OF 1ST-ROW AND 2ND-ROW ELEMENTS(1))

Configuration interaction calculations on various K-shell excited stat es of selected tetrahedral compounds of first- and second-row elements and for the corresponding states of their (Z + 1)-core analogue molec ules are performed. This model may open an opportunity to avoid extens ive calculations on K-shell excited states of larger molecules. Prior studies of the model have been restricted to the Hartree-Fock level of treatment, while the present work also accounts for a considerable po rtion of the correlation energy. The assignment of the states in the K -shell excited molecule and in its (Z + 1)-analogue as well as the ver tical term values of both species are compared. In addition, term valu es and relative intensities for the vertical transitions are compared with experimental results for the K-shell excited species. For the sec ond-row compounds, silane and PH4, the predictions of the (Z + 1)-mode l can be confirmed for all states considered within the limits of the errors given by the numerical method. The first-row compounds, methane and NH4, show some deviations from the core-analogy model, due to the smaller shielding of the core-hole, and particularly for states of ma inly valence character as well as for core-excited states with large s inglet-triplet splittings. In these cases the K-shell excited triplet states are in better accord with the doublet states in the (Z + 1)-rad ical than the K-shell excited singlet states.