Relaxation method

Relaxation methods are techniques in chemical kinetics used to measure the rates of extremely fast reactions — those that complete in milliseconds or microseconds — by perturbing a chemical system from equilibrium and observing how quickly it relaxes back. Developed by Manfred Eigen in the 1950s and 1960s, these methods earned him the Nobel Prize in Chemistry in 1967.

The principle is simple: a system at equilibrium is suddenly disturbed (by a rapid change in temperature, pressure, electric field, or pH), and the relaxation back to the new equilibrium is recorded spectroscopically. From the relaxation time constant, one can deduce the rate constants of the underlying reactions. The method treats chemical equilibrium as a dynamical system with a characteristic return time, making it a precursor to the modern study of nonequilibrium thermodynamics and dissipative structures.

Relaxation methods transformed physical chemistry by extending the measurable time range of reaction kinetics by orders of magnitude, enabling the study of processes such as proton transfer, enzyme-substrate binding, and the folding of small proteins.