Observation of a spin-protected high-energy isomer of Al4N- cluster

Photoelectron spectroscopy experiments combined with first-principles calcu lations based on generalized gradient approximation to the density function al theory show that an Al4N- anion cluster lying 0.97 eV above its ground-s tate structure can exist not because it is protected by an energy barrier b ut because it has a different spin multiplicity. Its existence is establish ed by comparing the calculated vertical electron detachment energies with t he experimental photo-detachment spectra. The electron affinity of Al3N, on the other hand, is anomalously low showing the characteristic of a closed- shell molecule and providing the signature of a monovalent Al, (C) 1999 Els evier Science B.V. All rights reserved.