Vibrational Relaxation Times in Nitrogen

By means of a technique involving an acoustical resonant cavity, the vibrational relaxation time in nitrogen has been measured at 1186, 1020, 778°K. The lifetime of an excited vibrational level in nitrogen at the above temperatures is found to be 2.29×106, 4.55×106, 6.55×106 collisions, respectively. These results are in good agreement with shock-tube measurements of Blackman in the temperature range of 3500–5600°K. The effect of water vapor on the relaxation time is discussed. Previous measurements by Huber and Kantrowitz are shown to have been affected by water vapor impurities; the present measurements are believed to be relatively free from this effect since the concentration of water vapor was at most 0.005%.