The problem of obtaining transition rates from acoustic measurements of vibrational-relaxation times is discussed. The error involved in using the Schäfer equation, τ1 = τ1C1/ΣiCi, to obtain the relaxation times for a single mode from the measured relaxation time is evaluated by calculating the sound absorption and dispersion from the reaction equations, using the method of Tanczos. The analysis shows that the absorption and dispersion curves closely approximate the single-relaxation-time curves in a series relaxation process, as long as the vibration-vibration (v-v) transfer is at least as fast as the vibration-translation (v-t) transfer. The calculations rule out a v-v process for the CO2/H2O interaction.