AB initio calculations of the electronic properties of N4− in KN3

Abstract

The energies of the ground state and low-lying excited states of the N4− defect in KN3 have been calculated using ab initio techniques. A rectangular equilibrium geometry with dimensions X = 2.76 and Z = 2.47 a.u. and ground state symmetry of Γ4+ was determined by calculating N4− as a free radical. For this ground state the unpaired electron is in a π orbital which is consistent with the experimental hyperfine tensor only if one edge of the N4− radical is parallel to the c axis in KN3. These results were used to calculate the X2Γ4+ state of N4− in the crystal field of KN3, yielding an energy of −217.899 Hartrees. The isotropic hyperfine constant was calculated to be a = 2.1 G and the components of the anisotropic hyperfine tensor as Bxx = −3.4 G, Byy = 7.0 G and Bzz = −3.6 G, in good agreement with experimental and INDO results. Several excited states were calculated for the N4− defect in KN3. When an estimate was made of the correlation energy, the transition energy of the X2Γ4+→A2Γ3− transition agreed well with the peak energy of the 780 nm absorption band which has been attributed to N4−.