Reaction of Cl with vibrationally excited CH4 and CHD3: State-to-state differential cross sections and steric effects for the HCl product

Abstract

Thermal and vibrationalstate selected rates of the CH4+Cl↔HCl+CH3 reaction J. Chem. Phys. 103, 9642 (1995); 10.1063/1.470731Core extraction for measuring statetostate differential cross sections of bimolecular reactionsThe mechanism for the reaction of atomic chlorine with vibrationally excited methane is investigated by measurement of correlated state and scattering distributions using the method of core extraction ͑see preceding paper͒. Laser photolysis of molecular chlorine creates monoenergetic chlorine atoms ͑Ͼ98% Cl 2 P 3/2 ͒ that react with vibrationally excited methane molecules prepared by linearly polarized infrared laser excitation. The resulting HCl product population distributions are determined by ͑2ϩ1͒ resonance-enhanced multiphoton ionization ͑REMPI͒, and the differential cross section for each product rovibrational state is measured by core extraction. Approximately 30% of the product is formed in HCl(ϭ1,J) with a cold rotational distribution; the remaining population is formed in HCl(ϭ0,J) and is more rotationally excited. We observe a rich variation of the scattered flux that is dependent on the internal-energy state of the product. The HCl͑ϭ1͒ product is sharply forward scattered for low J and becomes nearly equally forward-backward scattered for high J; the HCl(ϭ0,J) product is back and side scattered. The reactions of Cl with C-H stretch-excited methane ͑CH 4 ͒ and C-H stretch-excited CHD 3 are found to have similar angular and internal-state distributions. Observation of the spatial anisotropy of the HCl͑ϭ0, Jϭ3͒ product shows that significant vibrational excitation of the methyl fragment does not occur. The measured spatial anisotropy is most consistent with a model in which backscattered HCl͑ϭ0, Jϭ3͒ is formed in coincidence with slight methyl vibrational excitation and the forward-scattered HCl͑ϭ0, Jϭ3͒ is formed in coincidence with no methyl excitation. The approach of the attacking chlorine atom with respect to the C-H stretch direction can be varied by rotating the plane of polarization of the infrared excitation. A marked steric effect is observed in which Cl atoms approaching perpendicular to the C-H stretch preferentially yield forward-scattered HCl͑ϭ1͒ product. On the other hand, the reaction is weakly dependent on the rotational quantum state of CH 4 ( 3 ϭ1,J), and on the rotational polarization. The data are consistent with a model that has a widely open ''cone of acceptance'' in which the impact parameter controls the internal-state and scattering distributions of the HCl product.

H + CD4 Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

“…The anisotropic TOF profiles can be analyzed to estimate the amount of internal energy deposited into the coproduct by a method described in previous publications. 37,38 Isotropic and anisotropic TOF profiles were recorded for the H + CD 4 (ν ) 0) reaction over the collision energy range 1.2 to 2.2 eV using both HI and HBr as a photolytic precursor; however, here we focus only on E col ) 1.2 and 1.95 eV. Figure 3 presents the CD 3 TOF profiles and the derived lab-frame speed distributions for CD 3 (ν ) 0) at E col ) 1.2 eV, CD 3 (ν ) 0) at E col ) 1.95 eV, and CD 3 (ν 2 ) 1) at E col ) 1.95 eV.…”

Direct and Indirect Hydrogen Abstraction in Cl + Alkene Reactions

“…We use previously published correction factors [27][28] 29 Therefore, we use the v = 1 conversion factors to convert the v = 2 line strengths to population. We refer to these converted spectra as "intensity-corrected spectra" throughout the text.…”

Product rotational polarization: Stereodynamics of the reaction Cl(2P3/2)+CD4(v=0,j=0)→DCl(v′=0,j′=1)+CD3

“…[20][21][22] The enhanced reagent number densities achieved using these techniques, compared with those typically obtained in conventional crossed-molecular beam methods, have now enabled full state-to-state differential cross sections to be measured for the ClϩCH 4 reaction. [16][17][23][24][25] Blais and Truhlar 26 and Han et al 27 have studied the alignment of the product rotational angular momentum as a function of scattering angle using quasiclassical-trajectory Legendre moment method and provided many new and valuable results. Recently, Zare and co-workers 28 have applied the experimental technique of core extraction combined with resonance-enhanced multiphoton ionization ͑REMPI͒ with a polarized laser beam to probe the angular-momentum alignment of the DCl product of the reaction of Cl with CD 4 .…”