Do Vibrational Excitations of CHD3 Preferentially Promote Reactivity Toward the Chlorine Atom?

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Science  22 Jun 2007:
Vol. 316, Issue 5832, pp. 1723-1726
DOI: 10.1126/science.1142313

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The influence of vibrational excitation on chemical reaction dynamics is well understood in triatomic reactions, but the multiple modes in larger systems complicate efforts toward the validation of a predictive framework. Although recent experiments support selective vibrational enhancements of reactivities, such studies generally do not properly account for the differing amounts of total energy deposited by the excitation of different modes. By precise tuning of translational energies, we measured the relative efficiencies of vibration and translation in promoting the gas-phase reaction of CHD3 with the Cl atom to form HCl and CD3. Unexpectedly, we observed that C–H stretch excitation is no more effective than an equivalent amount of translational energy in raising the overall reaction efficiency; CD3 bend excitation is only slightly more effective. However, vibrational excitation does have a strong impact on product state and angular distributions, with C–H stretch-excited reactants leading to predominantly forward-scattered, vibrationally excited HCl.

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