The approximate force fields for a group of nitrogen halogen compounds like ONF3, NF3, NF2Cl, NFCl2, NF2D and NCl3 were studied using the kinematic methods of Herranz and Torkington. It was found that the application of Torkington's method yields a reliable set of potential energy constants consistent with other molecular constants. A linear relationship between the N -F bond stretching force constants and the bond order was found to exist. It was also found that the value of the N-F bond stretching force constant is proportional to the number of fluorine atoms substituted.