Measurements of vibration-vibration coupling in gas mixtures

Abstract

A series of experiments were performed on NO−CO, NO−N 2 and CO 2 −N 2 mixtures to measure the rate of vibration-vibration (V-V) energy exchange. The experiments were carried out behind incident shocks in shock tubes and cover the approximate temperature range from 800° to 3250°K. The vibrational relaxation of the gases was measured by following the time history of the infrared emission from the fundamental vibration-rotation bands of the IR active species. The experimental observations are that the component with the faster translation-vibration (T-V) energy exchange rate (NO or CO 2 in these mixtures) initially relaxes rapidly to some fraction of its final equilibrium vibrational energy. At this point the V-V process forces the two components to subsequently approach equilibrium with the same rate. Small concentrations of NO or CO 2 are shown to dramatically reduce the relaxation time of the major component, CO or N 2 . By using the vibrational energy relaxation equations for a binary gas mixture, including the effect of V-V exchange, the probability per collision of the V-V process has been determined from the vibrational relaxation data on these gas mixtures. These data, combined with other measurements, are shown to be in good agreement with the theoretical calculations in terms of both magnitude and temperature dependence.