How closely related are the effective and the real temperature

In the context of the kinetic method, the effective temperature is defined as being equal to the real temperature of a population of cluster ions in thermal equilibrium, which would yield the same product ratio as that observed in the mass spectrometric experiment. The effective temperature is not a thermodynamic quantity and depends not only on the internal energy content but also on the experimental conditions. A very good correlation has been found between the effective temperature and the mean internal energy of ions dissociating in the time window of analysis, but not with the mean internal (or excess) energy of the whole ion population. Calculations suggest that assuming a high internal energy is unnecessary for the kinetic method to be accurate. Care should be taken, however, in evalulating entropy effects and to check that the cluster ions studied have the same (or a similar) effective temperature.