Subject: free energy of activation

From: Atte Sillanpaa <[email-masked]>
Date: Wed, 15 Mar 2000 10:33:52 +0200

Hello CCLers,
I'm trying to calculate the free energy of activation for a process where
there is no minimum on the potential energy surface (PES). The (ethene
polymerisation termination) reaction begins with
a beta elimination from an alkyl group to the metal center. This forms a
fairly unstable metal hydride and a hapto2-alkene. The PES for scanning
the alkene away from the metal increases monotonically approaching the
separated products value. The free energy of separated products is readily
calculated, and is naturally much lower relative to PE. However, as the
alkene recedes from the metal it gradually gains the translational and
rotational degrees of freedom and its free energy drops, but there is a
maximum at some point.

The question is that if I calculate the free energy with the harmonic
approximation at some (ambigious) constrained geometry (distance from the
metal) is it of any approximate value for the free energy of activation?

Is there some other method for calculating the free energy of activation
in this kind of PES?

Thanks for the bandwidth, and I will summarise,

Atte

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