Crossed molecular beam study of the reactions of methyl bromide with potassium and rubidium

Journal Article · Fri Dec 15 04:00:00 EST 1978 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.436580· OSTI ID:6580895

Pang, H F; Wu, K T; Bernstein, R B

Using the crossed molecular beam method, the yields of the alkali halide product MBr from the exoergic reactions CH/sub 3/Br+M..-->..MBr+CH/sub 3/ (MequivalentK, Rb) have been measured as a function of relative translational energy up to 0.9 and 1.3 eV for K and Rb, respectively. Supersonic seeded beams of CH/sub 3/Br are crossed with thermal alkali beams and the in-plane angular distribution of MBr measured at different average relative translational energies E-bar/sub tr/. The reactions are found to have appreciable energy thresholds, 0.24 +- 0.06 and 0.20 +- 0.06 eV for the K and Rb-reactions, respectively. The product yields increase monotonically with E-bar/sub tr/ above threshold. The postthreshold energy dependence of the cross sections has been obtained by deconvoluting these data from the crossed beam velocity distributions. The MBr angular distributions are characteristic of a direct, rebound mechanism, with a large fraction of the available energy going into product translation. The average recoil energy E-bar'/sub tr/ of the product MBr increases linearly with E-bar/sub tr/ (dE-bar'/sub tr//dE-bar/sub tr/approx. =0.73). The present data for the M+CH/sub 3/Br systems are compared with previous results for the analogous CH/sub 3/I reactions and with predictions of several theoretical models. The significantly higher activation barriers for the CH/sub 3/Br reactions account for their smaller thermal reaction rate constants relative to the analogous CH/sub 3/I reactions (from early flame experiments).

• Research Organization: Chemistry and Physics Department, The University of Texas, Austin, Texas 78712 and Department of Chemistry, Columbia University, New York, New York 10027
• OSTI ID: 6580895
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 69:12; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALI METAL COMPOUNDS
ALKALI METALS
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
BEAMS
BROMIDES
BROMINATED ALIPHATIC HYDROCARBONS
BROMINE COMPOUNDS
COLLISIONS
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
METALS
METHYL BROMIDE
MOLECULAR BEAMS
MOLECULE COLLISIONS
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
POTASSIUM
POTASSIUM BROMIDES
POTASSIUM COMPOUNDS
RUBIDIUM
RUBIDIUM BROMIDES
RUBIDIUM COMPOUNDS