Vibrational Excitation in Some Four-Center Transition States

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Science  20 Nov 1964:
Vol. 146, Issue 3647, pp. 1045-1048
DOI: 10.1126/science.146.3647.1045


The rates of substitution of deuterium for hydrogen in homogeneous gas phase reactions between D2 and HX (X = H, Cl, NH2, or HS) were measured at high temperatures by single-pulse shock tube techniques. The magnitudes observed and their dependency on concentration indicate that the rates of exchange are much faster than would be attainable were the deuterium to dissociate and the D atoms to react with HX by atomic displacement to produce H + DX. Also, these rates were not limited by methathesis through four-center transition states generated by sufficiently energetic collisions between the principal reactants. The results are compatible with the assumption that the rates are controlled by the populations of D2 in about its 6th vibrational energy level.