How does chemical relaxation cause sound absorption in nitrogen tetroxide gas?

In nitrogen tetroxide ($N_2{O}_4$) gas, sound absorption occurs due to the finite rate at which the gas reaches chemical equilibrium when subjected to the oscillating pressure and temperature of a sound wave.1

As a sound wave propagates, it creates periodic fluctuations in pressure and temperature. Nitrogen tetroxide exists in an equilibrium between its dimer form ($N_2{O}_4$) and two monomer molecules of nitrogen dioxide ($N{O}_2$). Because the dissociation and association of these molecules are not instantaneous, the chemical system requires a finite amount of time—the relaxation time—to adjust to these changing conditions.1

At intermediate sound frequencies, the chemical equilibrium lags behind the pressure variations. This phase lag between the external disturbance and the system's response results in the dissipation of energy from the sound wave, which is observed as sound absorption. Maximum absorption occurs when the angular frequency of the sound wave is equal to the reciprocal of the relaxation time.1