The experimental potential energy curves for the different electronic states of astrophysically important LiS+ and NiS molecules are constructed by using Rydberg-Klein-Rees method as modified by Vanderslice et al. The ground state dissociation energies are determined by curve fitting techniques using the five parameters Hulburt-Hirschfelder (H-H) function. The estimated dissociation energies are 0.81__ampersandsignplusmn;0.02 and 3.56__ampersandsignplusmn;0.08 eV for LiS+, and NiS respectively. These values are in good agreement with the values reported in the earlier literature. The r-centroids and Franck-Condon factors (FC factors) for the bands of 3 -X3 - system of LiS+ and A3 -X3 - system for NiS, molecules have been calculated. The Franck-Condon factors are evaluated by the approximated analytical methods of Jarmain and Fraser. The absence of the bands of these systems is explained.