Previous measurements of sound absorption due to vibrational relaxation inCO2/D2Smixtures indicate a vibrational‐vibrational (v‐v) coupling between the bending mode ofCO2and the stretching modes ofD2S. A theory by Tanczos was used to analyze the results, but this theory did not allow for quantum changes greater than two in either one of the colliding molecules. Theoretical curves were calculated, therefore, for a v‐v coupling in which a two‐for‐one quantum exchange took place between the bending mode inCO2and the stretching modes inD2S. The theory has now been extended to treat cases where the v‐v coupling involves a three‐for‐one quantum exchange between modes. Using this theory, there is a slight improvement in the theoretical fit to the experimental absorption data onCO2/D2Smixtures. This is to be expected because of the near resonance between the 0310 level ofCO2and the 100 and 001 levels ofD2S.