The relaxation time for the appearance of translational energy from the ν3-mode of carbon dioxide and nitrous oxide, in mixtures with nitrogen, has been determined by the spectrophone. The results are consistent with relaxation times in the pure gases at 1 atm of 7.1 and 1.5 µsec respectively, and indicate that nitrogen can “trap” vibrational energy from carbon dioxide and also that nitrogen is relatively inefficient as a collision partner in de-exciting vibrational energy in these gases, though more inefficient in carbon dioxide than in nitrous oxide.