Editing Transition state (section)

== Observing transition states ==

Because the structure of the transition state is a first-order [[saddle point]] along a [[potential energy surface]], the population of species in a reaction that are at the transition state is negligible. Since being at a saddle point along the potential energy surface means that a force is acting along the bonds to the molecule, there will always be a lower energy structure that the transition state can decompose into. This is sometimes expressed by stating that the transition state has a ''fleeting existence'', with species only maintaining the transition state structure for the time-scale of vibrations of chemical bonds (femtoseconds). However, cleverly manipulated [[spectroscopy|spectroscopic]] techniques can get us as close as the timescale of the technique allows. [[Femtochemistry|Femtochemical]] [[IR spectroscopy]] was developed for that reason, and it is possible to probe molecular structure extremely close to the transition point. Often, along the reaction coordinate, [[reactive intermediate]]s are present not much lower in energy from a transition state making it difficult to distinguish between the two.