Isotope effects in hot atom abstraction reactions of H* and D* with CH/sub 3/CD/sub 3/. [Initial hot atom energy range of 1. 1 to 2. 9 eV]

Journal Article · Thu Sep 09 04:00:00 EDT 1976 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100560a003· OSTI ID:7248906

Beverly, G D; Martin, R M

Hot H and D (H* and D*) reactions with ethane were studied in Br/sub 2/ scavenged systems using HBr and DBr as photodissociation hot atom sources. Quantum yields for the abstraction reactions of H* + C/sub 2/D/sub 6/ and H* + CH/sub 3/CD/sub 3/ were determined at an initial hot atom energy E/sub i/ = 1.6 eV, and found to be in good agreement with previous yields determined by the integral reaction probability method. Abstraction isotope effects for H* and D* + CH/sub 3/CD/sub 3/ were determined over the range E/sub i/ = 1.1 to 2.9 eV, in 94 percent ethane systems. With H* + CH/sub 3/CD/sub 3/ the H/sub 2//HD product ratio increased from 2.4 +- 0.1 at 1.1 eV to 2.8 +- 0.1 at 2.9 eV, whereas with D* + CH/sub 3/CD/sub 3/ the HD/D/sub 2/ product ratio was approximately constant with change in E/sub i/, 2.0 +- 0.1 at 1.6 eV and 1.9 +- 0.1 at 2.0 and 2.9 eV. In mixtures with a large mole fraction of Br/sub 2/ to scavenge low energy atoms the isotope effects at E/sub i/ = 2.9 eV increased to 3.1 +- 0.1 for H* + CH/sub 3/CD/sub 3/ and 2.8 +- 0.4 for D* + CH/sub 3/CD/sub 3/. These results, taken together with a previous determination of the abstraction isotope effect in the T* + CH/sub 4/--CD/sub 4/ system at 2.9 eV, give a consistent trend favoring H over D abstraction, with the H/D isotope effect increasing with decreasing hot atom mass. It is concluded that both the H/D preference and the hot atom mass effect can be understood in terms of inertial considerations and that a zero point energy effect may also contribute to the H/D preference.

• Research Organization: Univ. of California, Santa Barbara
• OSTI ID: 7248906
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 80:19; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400302 -- Organic Chemistry-- Isotope Effects-- (-1987)
400701* -- Radiochemistry & Nuclear Chemistry-- Hot-Atom Chemistry
ALKANES
BROMINE
CHEMICAL REACTIONS
CHEMISTRY
CRYOGENIC FLUIDS
DEUTERIUM
ELEMENTS
ETHANE
FLUIDS
HALOGENS
HOT ATOM CHEMISTRY
HYDROBROMIC ACID
HYDROCARBONS
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INORGANIC ACIDS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
NONMETALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RADIOCHEMISTRY
SCAVENGING
STABLE ISOTOPES
YIELDS