For the Relaxed Excited States of the F-centre, the simplest vibronic model involves only the Γ−4; mode in the electron-lattice interaction HeL. In analyzing the perturbation correction due to HeL, Ham and Grevsmühl kept only the linear terms in the coupling constant G and ended up with a positive value for the field-induced shift in the energy of the parallel component in emission δE∥,—in disagreement with the experiments. In this paper, it is shown that when the perturbation correction terms are kept up to G2, δE∥, is negative.