A geometric parameter that changes during the conversion of one (or more) reactant @[email protected] into one (or more) product molecular entities and whose value can be taken for a measure of the progress of an @[email protected] (for example, a @[email protected] or bond @[email protected] or a combination of bond lengths and/or bond angles; it is sometimes approximated by a non-geometric parameter, such as the @[email protected] of some specified bond). In the formalism of '@[email protected]', the reaction coordinate is that coordinate in a set of curvilinear coordinates obtained from the conventional ones for the reactants which, for each @[email protected], leads smoothly from the configuration of the reactants through that of the @[email protected] to the configuration of the products. The reaction coordinate is typically chosen to follow the path along the @[email protected] (path of shallowest ascent/deepest descent) of potential energy from reactants to products. The term has also been used interchangeably with the term @[email protected], applicable to the coordinate in the immediate vicinity of the potential energy maximum. Being more specific, the name @[email protected] is to be preferred in that context.
potential-energy reaction surface,
minimum-energy reaction path