Editing Activated complex (section)

=== Symmetry ===
An activated complex with high symmetry can decrease the accuracy of rate expressions.<ref name=":1">{{Cite journal |last=Murrell |first=J. N. |last2=Laidler |first2=K. J. |date=1968 |title=Symmetries of activated complexes |url=https://pubs.rsc.org/en/content/articlelanding/1968/tf/tf9686400371 |journal=Transactions of the Faraday Society |language=en |volume=64 |issue=0 |pages=371–377 |doi=10.1039/TF9686400371 |issn=0014-7672|url-access=subscription }}</ref> Error can arise from introducing [[symmetry number]]s into the [[rotational partition function]]s for the reactants and activated complexes. To reduce errors, symmetry numbers can by omitted by multiplying the rate expression by a statistical factor:

<math display="block">k = l^\ddagger \frac{k_\text{B} T}{h} \frac{Q_\ddagger}{Q_A Q_B} e^{-\frac{\varepsilon}{k_\text{B} T}}</math>

where the statistical factor <math display="inline">l^\ddagger</math> is the number of equivalent activated complexes that can be formed, and the ''Q'' are the [[Partition function (statistical mechanics)|partition functions]] from the symmetry numbers that have been omitted.<ref name=":1" />

The activated complex is a collection of molecules that forms and then explodes along a particular internal normal coordinate. Ordinary molecules have three translational [[Degrees of freedom (physics and chemistry)|degrees of freedom]], and their properties are similar to activated complexes. However, activated complexed have an extra degree of translation associated with their approach to the energy barrier, crossing it, and then dissociating.<ref name=":2" />