| These experiments explore energetic influences on the reactions of stretch-excited CH3D with Cl though the modification of the collisional energy in the reactive system. A second set of experiments explores the influence of changing the radical reactant on the reaction stretch-excited CH4 with Cl or Br. In the CH3D reactions, we prepare methane in the |110⟩|0⟩ eigenstate using direct absorption of infrared light near 6000 cm-1. In the latter pair of reactions, we prepare the methane in the |1100⟩, | 2000⟩, |1000⟩ + nu2 + nu4, and 3nu2 + nu4 eigentstates using direct absorption of infrared light between 5830--6070 cm -1. We monitor the vibrational states of the CH2D and CH3 products we produce via (2 + 1) resonance enhanced multiphoton ionization. In the reaction with CH3D, we find that CH3 production is shut off at the lowest collisional energies, ultimately leading to a reassessment of both the H- and D-abstraction barriers. We find that barriers of 1198 cm-1 and 1555 cm-1, values based on calculations by Czako and Bowman (J. Chem. Phys., 136 , 044307 (2012)), match our experimental results for the reaction of CH3D with Cl. We additionally find energetically-dependent reactivity differences for several rotational states between the lowest collisional energies (the result of 416 nm photolysis) and the higher two collisional energy distributions (from 355 nm and 309 nm photolysis). In the reactions of chlorine atoms with CH4, we find surprising reactivity for transitions that apparently excite E-state rotations in the 6041 cm-1 region. Excitation of these transitions produces approximately 10--100 times more reactivity than excitation of the nearby, dominant F2 features. We observe the first infrared-driven reactions with bromine atoms and find confirmation for the spectator bond picture, that excited, but unreacted oscillators carry their excitation through the (un)reactive encounter. |
