Decomposition threshold, critical

In Equation 4, AEm is the average internal energy transferred from excited species A upon collision with M, which may be either nonreactive bath gas or reactant molecules, and ka(E ) is the RRKM rate constant for imimolecular decomposition calculated at each energy E. Eventually after successive energy degrading collisions without unimolecular decomposition the excited molecule may be stabilized to an energy level below the critical decomposition threshold Ec. 

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