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At "infinite" pressure, where 1 /[M] = 0, the rate constant should have its high-pressure limiting value. It is seen that this high-pressure limiting value, k^, is equal to k.d. One would also qualitatively expect = k.d from the reaction scheme consisting of (12), (-12), and (13); thus in the limit of infinite pressure, all the energized adducts formed in (12) will be stabilized in (13) and none will have a chance to decompose back to reactants via (—12). In this case, the rate constant will just be that for formation of HOSOf, that is, k.d.

This approximate treatment of termolecular reactions can also be used to examine how the third-order, low-pressure rate constant km relates to the rate constants k.d, kh, and /cc. for the elementary reactions assumed to be involved. As [M] approaches zero, k.^ approaches &a/cc[M]//cb, so that is given by un =

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