Control of bimolecular reactions: Bond-selected reaction of vibrationally excited CH3D with Cl (2P3/2)

Selective vibrational excitation permits control of the outcome of a reaction with two competing channels. The thermal reaction of CH3D with Cl (2P3/2) yields two reaction products: CH3 from the D-atom abstraction and CH2D from the H-atom abstraction. We prepare the first overtone of the C–D stretching vibration (2ν2) at ∼4300 cm−1 and react the vibrationally excited molecule with photolytic Cl atoms. The 2+1 resonance enhanced multiphoton ionization spectra for the products show that the 2ν2 vibrational excitation of CH3D exclusively increases the probability of breaking the C–D bond, yielding CH3 but no CH2D. By contrast, vibrational excitation of the combination of the antisymmetric C–H stretch and CH3 umbrella (ν4+ν3) vibrations, which has total energy similar to that of 2ν2, preferentially promotes the H-atom abstraction reaction to produce CH2D over CH3. The vibrational action spectra for the two products permit the separation of the two sets of interleaved transitions to give band origins and rotational constants of the 2ν2 state and the ν4+ν3 state of CH3D.