Rapid energy exchange limit

Price, W.D. Williams, E.R. Activation of peptide ions by blaekbody radiation Factors that lead to dissociation kinetics in the rapid energy exchange limit. J. Phys. Chem. A 1997, lOI, 8844-8852. 

Paech K, Jockusch RA, Williams ER (2002) Slow infrared laser dissociation in the rapid energy exchange limit. J Phys Chem A 106 9761-9766... 

Two limiting cases of this C3(-H) or C3(-D) elimination chemistry are possible. In one mechanism, rapid energy input into the C-H/D reaction coordinate suggests that an excess of energy, beyond the barrier height, can occur. Here one expects a nearly statistical distribution of reaction pathways. Thus, the deuterium number (deuterium exchange fraction) should be 0.5. At more moderate vibrational... 

The rate of exchange was too rapid for Leifer to measure quantitatively at that time (equilibrium was reached within 15 sec), and he could only establish a lower limit of 103 A/-1 sec-1 for the rate constant k2 at 238°K. Although he concluded that the activation energy for the reaction had to be less than 1 kcal/mole, the data afford no compelling reason why it cannot be as great as 10 kcal/mole. Such a large value is unlikely, however. 

From the data available, an upper limit of 10 kcal/mole can be set for the process, suggesting that the dissociation energy for the Ga—CH=CH2—Ga bridge is substantially less than that observed for the aluminum systems. This fact may account for the more rapid exchange reactions observed. 

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