eiArrheniuksellista

eiArrheniuksellista is a term used primarily in the field of chemical kinetics to describe processes that do not obey the Arrhenius temperature dependence. The Arrhenius equation, which relates the rate constant of a reaction to temperature through an exponential term containing the activation energy, is a foundational concept for many reaction rate studies. When experimental data deviate systematically from the linear behavior predicted by the logarithm of the Arrhenius equation, the phenomenon is referred to as eiArrheniuksellista. It is often encountered in complex catalytic systems, surface reactions, or in reactions that involve multiple mechanistic steps where distinct temperature-dependent sites compete.

The word originates from the Finnish language, combining ei (“not”) with Arrheniuksellista, the adjectival form of Arrhenius. The expression is employed in scientific literature to emphasize that a particular reaction rate or equilibrium constant shows anomalous temperature behavior. This can be a sign of a change in mechanism, opening of new reaction channels, or a substantial modification of the transition state structure with temperature.

Typical examples include oxidation reactions on metal surfaces where the rate increases more slowly or even decreases at higher temperatures, or polymerization processes that exhibit a bell-shaped temperature dependence. In such cases, kinetic analysis may involve alternative models such as Bell-evans or transition state theory with temperature-dependent activation enthalpies and entropies.

eiArrheniuksellista is relevant for researchers designing temperature-controlled processes, interpreting kinetic data, and for computational chemists who model temperature-dependent potential energy surfaces. By identifying and characterizing non‑Arrhenius behavior, scientists can uncover underlying mechanistic details that are obscured when assuming a simple Arrhenius framework.