Reactive cross section as a function of reagent energy. II. H(D)+HBr(DBr). -->. H/sub 2/(HD,D/sub 2/)+Br

Journal Article · Mon Jun 01 00:00:00 EDT 1981 · J. Chem. Phys.; (United States)

OSTI ID:6498679

Hepburn, J W; Klimek, D; Liu, K; Macdonald, R G; Northrup, F J; Polanyi, J C

A crossed molecular beam study has been made of reactive cross section as a function of collision energy S/sub r/(E/sub T/) for all isotopic variants of the abstraction reaction H'+H''Br..-->..H'H''+Br. The apparatus incorporates, for reagent preparation, a supersonic source of variable-energy H or D atoms, and, for product detection, a tunable vacuum ultraviolet laser to obtain laser-induced fluorescence of Br. The cross-section functions indicate that the threshold energy for reaction is <1 kcal/mol. At enhanced collision energy of E/sub T/ = 7 kcal/mol, the observed order of reactivity in the isotopic series designated (H',H'') was (D,H)> or approx. =(D,D)>(H,H)>(H,D). As noted in a previous report from this laboratory (Int. J. Chem. Kinet., Laidler Festschrift (in press)) the favorable kinematics for (D,H) as compared with (H,D) can be understood in terms of lengthened interaction time for D atom reaction (compared with H) and diminution in the time required for HBr (compared with DBr) to rotate into the preferred alignment for reaction. The effect is illustrated here in terms of a simple model of reaction. The experimental data obtained in this work at low collision energy, in conjunction with 300 K rate constants obtained by others, suggest that close to threshold, kinematic effects are supplanted by threshold effects, yielding S/sub r/(H,D)>S/sub r/(D,H), the inverse of the principal isotope effect at enhanced collision energy.

• Research Organization: Department of Chemistry, University of Toronto, Toronto, Canada M5S 1A1
• OSTI ID: 6498679
• Journal Information: J. Chem. Phys.; (United States), Vol. 74:11
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
HYDROBROMIC ACID
ATOM-MOLECULE COLLISIONS
CHEMICAL REACTIONS
HYDROGEN
CROSS SECTIONS
ENERGY DEPENDENCE
EXPERIMENTAL DATA
MOLECULAR BEAMS
ATOM COLLISIONS
BEAMS
COLLISIONS
DATA
ELEMENTS
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
MOLECULE COLLISIONS
NONMETALS
NUMERICAL DATA
640304* - Atomic
Molecular &amp; Chemical Physics- Collision Phenomena