Why does the monomer-dimer ratio lag behind a rapidly changing sound wave?

The monomer-dimer ratio lags behind a rapidly changing sound wave because chemical systems cannot respond instantaneously to external disturbances.1

When a sound wave propagates through a gas like nitrogen tetroxide, it creates a sinusoidal variation of pressure and temperature. While the reactivities of the monomers and dimers change immediately with these fluctuations, the actual concentrations of the molecules change at a finite rate determined by the system's chemical equilibrium kinetics.1

If the sound frequency is high, the pressure oscillates too rapidly for the dissociation and association reactions to re-establish equilibrium in time. This delay, known as the relaxation time, results in the monomer-dimer ratio trailing behind the pressure variation. At intermediate frequencies, this lag causes sound absorption and dispersion, which physicists use to calculate the reaction rates and mechanisms.12