The reaction of Cl atoms with CH3D proceeds either by abstraction of hydrogen to produce HCl + CH2D or by abstraction of deuterium to produce DCl + CH3. Using Cl atoms with different amounts of translational energy, produced by photolysis of Cl2 with 309, 355, or 416 nm light, reveals the influence of translational energy on the relative reaction probability for the two channels. These measurements give an estimate of the energy barrier for the reaction for comparison to theory and indicate that tunneling is the dominant reaction mechanism at low collision energies. Adding two quanta of C-H stretching vibration causes the reaction to proceed readily at all collision energies. Detecting the vibrational state of the CH2D product shows that vibrational energy initially in the surviving C-H bond appears as vibrational excitation of the product, an example of spectator behavior in the reaction. The reaction produces both stretch and stretch-bend excited products except at the lowest collision energy. A subtle variation in the reaction probability of the lowest energy rotational states with translational energy may reflect the presence of a van der Waals well in the entrance channel.

In an effort to understand how the Polanyi rules can be extended from radical-diatomic molecule reactions to radicalpolyatomic molecule reactions, members of the bimolecular gas-phase dynamics community have often used H-atom abstraction from methane (or one of its isotopologues) by X (where X=H, F or Cl) as a model system. Each of these model reactions can be separately characterized by both the height and location of the potential energy barrier along the reaction coordinate. Currently, we are working to understand the gas-phase dynamics of H-atom abstraction from CH 4 when X=Br. In this iteration of the model system, the abstraction barrier is located very late along the reaction coordinate and is quite high by comparison to other studied systems. This leads to some surprising dynamical effects in the X=Br system that we have not seen in other systems studied thus far.