Activation and Dissociation of Ions

Thus far very little has been said about how precursor ions, including the intact ionized molecules formed by soft  

Both of these factors are contained in the following ultra-simple expression for the unimolecular dissociation rate constant for isolated ions (molecules) (i.e. no thermal equilibrium among large numbers of such species)  

In practice the situation is more complex. It is necessary to take into account the average value of Ej , reached by the particular ion activation method used, and also the timescale available for reaction to occur (in general longer for a tandem-in-time (trapping) instrument than for a tandem-in-space (beam) instrument), which in turn determines the range of values of that can produce 

The efficiency with which the translational (kinetic) energy of the ion/molecule collision is transformed into internal energy in the collisional activation step is a highly complex problem but it is possible to understand some practically important aspects in a relatively simple fashion. The objective is to increase Ej to a value sufficiently greater than Ej , that fragmentation proceeds at a rate sufficient to provide a useful )deld of the product 

Center of Mass Collision Energy The Maximum Fraction of the Relative Kinetic Energy Between Two Objects that can he Transformed into Internal Energy 

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