Molecular Orbitals of (NH₄)₂SO₄:Tl

Abstract

One electron molecular orbital(MO) energy levels of Tl-(SO 4 ) n complexes in (NH 4 ) 2 SO 4 have been calculated by using the charge-consistent extended Hückel method at various temperatures from 25 to -140°C. The calculation has been performed both for the ground and excited states, and the result shows that the highest occupied MO in the ground state, s ', mainly consists of the thallous 6 s orbital, and the lowest three partially occupied MO's in the excited state, p ' * 1,2,3 , consist of the thallous 6 p orbitals. The optical absorption bands of (NH 4 ) 2 SO 4 :Tl are attributed to the transitions between MO's, s ' and p ' * 1,2,3 . The temperature dependence of the absorption spectra is explained by that of both the energies of MO's and the crystal fields of(NH 4 ) 2 SO 4 crystals.