I am studying a reaction using electronic structure methods using various software packages (ORCA,GAMESS, G09) and have found two possible transition structures between product and reactant. Both have imaginary frequencies, but each has a different energy value, frequencies and geometries. Some software coincide in the found transition state while other differs, adding to the confusion. So my questions are:
Is it possible to have multiple transition states, if so what is a good criteria to choose between candidate states?
Should I expect the frequency to be within certain range? (for example if the reaction is the movement of a H atom within the molecule)
Is there some quantitative value(s) (energy, vibration amplitude/frequency, vibration 3d direction vectors, 3d geometry, etc.) that can be used as a reasonable measure to choose the "correct" state? (That is to avoid visualizing the imaginary mode of vibration or computing the IRC).