Core molecular orbital contribution to N2O isomerization as studied using theoretical electron momentum spectroscopy

Core molecular orbital contribution to the electronic structure of N2O isom ers has been studied using quantum mechanical density functional theory com bined with a plane wave impulse approximation method. Momentum distribution s of wave functions for inner shell molecular orbitals of the linear NNO, c yclic and linear NON isomers of N2O are calculated through the (e, 2e) diff erential cross sections in momentum space. This is possible because this mo mentum distribution is directly proportional to the modulus squared of the momentum space wave function for the molecular orbital in question. While t he momentum distributions of the NNO and cyclic N2O isomers demonstrate str ong atomic orbital characteristics in their core space, the outer core mole cular orbitals of the linear NON isomer exhibit configuration interactions between them and the valence molecular orbitals. It is suggested that the f rozen core approximation breaks down in the prediction of the electronic st ructure of such an isomer. Core molecular orbital contributions to the elec tronic structure can alter the order of total energies of the isomers and l ead to incorrect conclusions of the stability among the isomers. As a resul t, full electron calculations should be employed in the study of N2O isomer ization. (C) 2001 Elsevier Science B.V. All rights reserved.