Effect of Several Light Molecules on the Vibrational Relaxation Time of Oxygen

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Abstract
Measurements of vibrational relaxation times of O2–H2, O2‐D2, and O2–He mixtures have been carried out by means of an acoustic resonance tube. It was found that all these light elements shorten the vibrational relaxation time of oxygen with H2 being by far the most effective. Surprisingly, D2 and He produced almost identical effects, indicating that molecular mass is the dominating factor in the ability of these gases to excite vibration in O2. Results of these measurements show that an O2–H2 collision is 2.96×103, an O2‐D2 collision 2.96×102, and an O2–He collision is 3.53×102 more effective than an O2–O2 collision. Most extensively studied was O2–H2, for which relaxation times were measured in eight different mixtures, the maximum concentration of H2 being 2.64% and the minimum 0.072%. Variation of the relaxation frequency with H2 concentration was linear, indicating that binary collisions alone are important. Extrapolation of this data to zero concentration gives a relaxation time for pure O2 of approximately 1.8×10−2 sec which is considerably longer than that obtained by other investigators. Comparison of the experimental data with theory suggests that the variation of intermolecular forces in the interaction of light elements with oxygen is much less steep than one would predict from a knowledge of the interaction forces in the separate similar interactions.

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