PNNL

Abstract

The electronic and geometrical structures of Al7N– are investigated using photoelectron spectroscopy and ab initio calculations. Photoelectron spectra of Al7N– have been obtained at three photon energies with seven resolved spectral features at 193 nm. The spectral features of Al7N– are relatively broad, in particular for the ground state transition, indicating a large geometrical change from the ground state of Al7N– to that of Al7N. The ground state vertical detachment energy is measured to be 2.71 eV, whereas only an upper limit of ~1.9 eV can be estimated for the ground state adiabatic detachment energy due to the broad detachment band. Global minimum searches for A7N– and Al7N are performed using several theoretical methods. Vertical electron detachment energies are calculated using three different methods for the lowest energy structure and compared with the experimental data. Excellent agreement is observed between the calculated results and the experimental data. The global minimum structure of Al7N– is found to possess C3v symmetry, which can be viewed as an Al atom capping a face of a N-centered Al6N octahedron. However, in the ground state of Al7N the capping Al atom pushes in to form a bond with the central N atom, significantly expanding the three neighboring Al atoms. Thus, even though Al7N still possesses C3v symmetry, it is better viewed as a N coordinated by seven Al atoms in a cage-like structure. The chemical bonding in Al7N– is discussed on the basis of molecular orbital and natural bond analyses.