The structure of the V centre produced by KrCl excimer laser irradiation of KI crystals at low temperatures

Abstract

KrCl excimer laser irradiation (hv = 5·58 eV) of KI single crystals at about 150 K produces F, F′, α, β and V centres. The V centres give rise to V2 and V3 bands which exhibit <100>-type dichroism. In KI crystals containing the V centres, the 111 cm-1 Raman line originating in the symmetric stretching vibration mode of an I- 3 molecular ion appears. On the basis of the I- 3 molecular ion model for the V centre, the V2 and V3 bands are considered to be due to relatively stronger transitions from the ground 1Σg0(σ2 uπ4 uσ2 gπ*4 u) state to the excited 1Σu0(σ2 uπ4 uπ4 gσgπ*4 uσ*u) and 3Πu0(σ2 uπ4 uπ3 gσ2 gπ*4 uσ*u) states respectively. The splitting of these two bands is ascribed mainly to the spin-orbit interaction. The deviation from a linear array of the I- 3 molecular ion bound by a cation vacancy is discussed from the experimental viewpoint of Raman scattering and optical absorption.