ABSTRACT
Transient, or time-resolved, techniques measure the response of a substance after a rapid perturbation. A swift ‘kick’ can be provided by any means that suddenly moves the system away from equilibrium-a change in reactant concentration, for instance, or the photodissociation of a chemical bond. Kinetic properties such as rate constants and amplitudes of chemical reactions or transformations of physical state taking place in a material are then determined by measuring the time course of relaxation to some, possibly new, equilibrium state. Determining how the kinetic rate constants vary with temperature can further yield information about the thermodynamic properties (activation enthalpies and entropies) of transition states, the exceedingly ephemeral species that lie between reactants, intermediates and products in a chemical reaction.
