Mode-and bond-selective reaction of Cl(~2P_(3/2)) with CH_3D:C-H stretch overtone excitation near 6000 cm~(-1)

摘要

Experiments explore the influence of different C-H stretching eigenstates of CH_3D on the reaction of CH_3D with Cl(~2P_(3/2)).We prepare the |110>|0>(A_1,E),|200>|0)(E),and |100>|0>+V_3+V_5 eigenstates by direct midinfrared absorption near 6000 cm~(-1).The vibrationally excited molecules react with photolytic Cl atoms,and we monitor the vibrational states of the CH_2D or CH_3 radical products by 2+1 resonance enhanced multiphoton ionization.Initial excitation of the |200>|0>(E) state leads to a twofold increase in CH_2D products in the vibrational ground state compared to 100>|0>+v_3+v_5 excitation,indicating mode-selective chemistry in which the C-H stretch motion couples more effectively to the H-atom abstraction coordinate than bend motion.For two eigenstates that differ only in the symmetry of the vibrational wave function,|110>|0>(A_1) and |110>|0>(E),the ratio of reaction cross sections is 1.00+-0.05,showing that there is no difference in enhancement of the H-atom abstraction reaction.Molecules with excited local modes corresponding to one quantum of C-H stretch in each of two distinct oscillators react exclusively to form C-H stretch excited CH_2D products.Conversely,eigenstates containing stretch excitation in a single C-H oscillator form predominantly ground vibrational state CH_2D products.Analyzing the product state yields for reaction of the |110>|0>(A_1) state of CH_3D yields an enhancement of 20+-4 over the thermal reaction.A local mode description of the vibrational motion along with a spectator model for the reactivity accounts for all of the observed dynamics.