Why was chemical relaxation difficult to detect experimentally before the second half of the 20th century?

Before the second half of the 20th century, chemical relaxation was difficult to detect because researchers lacked the necessary technical capabilities to observe processes that occur on extremely short timescales. While the theoretical basis for chemical relaxation was suggested as early as 1910, experimental detection remained unfeasible for decades.1

During the first half of the 20th century, scientific efforts in the field of relaxation were primarily focused on physical processes, such as dielectric relaxation or energy transfer between molecular degrees of freedom. Furthermore, traditional methods for studying chemical kinetics faced significant limitations: the time required to mix reactants or alter system conditions was often comparable to or longer than the half-life of the reactions being studied, making accurate measurement impossible.12

It was not until the 1950s that Manfred Eigen rediscovered and developed relaxation techniques, such as the temperature-jump method, which allowed scientists to disturb a system already at equilibrium and measure the rapid return to a new equilibrium state. These technological advancements finally enabled the study of extremely fast chemical reactions.123