CH Stretching Excitation in the Early Barrier F + CHD3 Reaction Inhibits CH Bond Cleavage
Weiqing Zhang, Hiroshi Kawamata, Kopin Liu*
Science, 325, 303-306 (2009)
Most studies of the impact of vibrational excitation on molecular reactivity have focused on reactions with a late barrier (that is, a transition state resembling the products). For an early
barrier reaction, conventional wisdom predicts that a reactant’s vibration should not couple efficiently to the reaction coordinate and thus should have little impact on the outcome. We report
here an in-depth experimental study of the reactivity effects exerted by reactant C-H stretching excitation in a prototypical early-barrier reaction, F + CHD3. Rather counterintuitively, we find
that the vibration hinders the overall reaction rate, inhibits scission of the excited bond itself (favoring the DF + CHD2 product channel), and influences the coproduct vibrational distribution
despite being conserved in the CHD2 product. The results highlight substantial gaps in our predictive framework for state-selective polyatomic reactivity.