2) Kinetic shift. If we would impart an amount of energy just equal to E0, the ions would require a much longer time to fragment than the time the ions take to travel from the source to the mass analyzer. This is because the total internal energy E is redistributed among all vibrational degrees of freedom of the ion (N = number of atoms; DOF = 3N-6), while only a single combination of vibrations leads to dissociation. It is hard to estimate the ion residence time; in most electrospray sources, a crude estimation is that the time scale for dissociation  = 10 -4 s. The kinetic shift (ks) is the difference between E0 and the actual appearance energy Eapp (Eapp = E0 + ks), the energy above which the dissociation rate constant k is equal to 1/.