Mode- and bond-selective reaction of Cl(P3∕22) with CH3D: C–H stretch overtone excitation near 6000cm−1

Abstract

Experiments explore the influence of different C-H stretching eigenstates of CH3D on the reaction of CH3D with Cl(2P3/2). We prepare the mid |110>|0>(A1,E), mid |200>|>0(E), and mid |100>|0> +nu3 +nu5 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 CH2D or CH3 radical products by 2+1 resonance enhanced multiphoton ionization. Initial excitation of the |200>|0>(E) state leads to a twofold increase in CH2D products in the vibrational ground state compared to|100>|0> +nu3 +nu5 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>(A1) 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 CH2D products. Conversely, eigenstates containing stretch excitation in a single C-H oscillator form predominantly ground vibrational state CH2D products. Analyzing the product state yields for reaction of the |110>|0>(A1) state of CH3D 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.

Quantum dynamics of polyatomic dissociative chemisorption on transition metal surfaces: mode specificity and bond selectivity

“…Lower panel: single-site RPH dissociation probabilities for CH 4 initially excited to antisymmetric stretch (1 0 (red) and 1 00 (brown)) and symmetric stretch (3 0 (blue)) states on Ni (100) View Article Online methane and atomic reactants such as H and Cl in the gas phase, 187 where mode specific and bond selective chemistry is well established. [188][189][190][191][192][193][194][195][196] Finally, we note in passing that Harrison and coworkers have advanced a statistical approach to methane DC processes. [197][198][199] While reproducing many observed properties, the statistical models are fundamentally incompatible with the mode specific dynamics supported by the overwhelming experimental and theoretical evidence.…”

Velocity map imaging the dynamics of the reactions of Cl atoms with neopentane and tetramethylsilane

“…[21][22][23][24][25][26][27][28][29][30][31][32] The experimental measurements and dynamical calculations for H-atom abstraction reactions involving simple alkanes illustrate a wealth of dynamical behaviour. For example, the shape of the transition state, with near linear Cl-H-C moiety, is reflected in the low rotational excitation of HCl products; scattering angles are largely determined by impact parameter and their distributions can vary with product rotational and vibrational quantum states; 1 and the reactions of Cl atoms with methane and partially deuterated isotopologues exhibit reagent vibrational mode specificity, [4][5][6][7][9][10][11][12]14,15,[33][34][35][36][37][38][39][40] electronically non-adiabatic pathways, 29,31,41,42 and evidence for scattering resonances. 43 Reactions of functionalized organic molecules (RH = alcohols, 24,44,45 amines, 46 alkyl halides 23,47 and linear and cyclic ethers 24,44,…”

Adiabatic and nonadiabatic dynamics in the CH3(CD3)+HCl reaction

“…The reverse reaction of Cl atoms with CH 4 ͑and isotopologs resulting from partial or complete deuteration͒ is well established as a benchmark polyatomic reactive system for studying scattering and vibrational mode and bond specific dynamics. [15][16][17][18][19][20][21][22][23][24] Reaction of Cl * with CH 4 adiabatically correlates with an electronically excited state of the CH 3 radical, and nonadiabatic formation of the energetically accessible CH 3 ͑X 2 A 2 Љ͒ + HCl products is not observed for collisions with energies just above the energetic barrier 25,26 but does occur at much higher collision energies. 27 In studies of the kinetics of collisional processes between Cl * atoms and small hydrocarbons, Matsumi et al 28 demonstrated that the rate of SO quenching of Cl * to grounda͒ Present address: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan.…”