MODE is used in the EF routine. Normally the default MODE=1 is used to locate a transition state, but if this is incorrect, explicitly define the vector to be followed by using MODE=n. (MODE is not a recommended keyword). If you use the FORCE option when deciding which mode to follow, set all isotopic masses to 1.0. The normal modes from FORCE are normally mass-weighted: this can mislead. Alternatively, use LARGE with FORCE: this gives the force constants and vectors in addition to the mass-weighted normal modes.