Parameters of activation barriers from curved arrhenius plots: X + H/sub 2/. -->. XH + H

Journal Article · Thu Mar 12 04:00:00 EST 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100290a059· OSTI ID:6868796

Furue, H; Pacey, P D

Expressions have been fitted by least-squares methods to experimental rate constants, k, as a function of temperature, T, for the gas-phase reactions of H, D, O, and F with H/sub 2/ and D/sub 2/. The heat capacities of activation were found to be between 6 and 42 J K/sup -1/ mol/sup -1/. The following expression, incorporating a factor, kappa(E/sub e/, T/T*), for tunneling through an unsymmetrical Eckart barrier of effective height E/sub e/, was capable of fitting the data within experimental uncertainty: k = kappa(E/sub e/, T/T*)AT/sup n/ exp(-E/sub e//(RT)). Here A, E/sub e/, and T*, the characteristic tunneling temperature, were adjustable parameters; n was fixed to match the heat capacity of activation contributed by translation, rotation, and vibration at the median experimental temperature. Experimental data for three reactions were not sufficiently extensive or consistent to provide reliable parameter values. Eleven out of fifteen parameters for five reactions (D, O, and F with H/sub 2/, O and F with D/sub 2/) agreed within about one standard deviation (0.04 to 0.1 log units for A, 0.6 to 2 kJ mol/sup -1/ for E/sub e/, 46 to 170 K for T*) with values calculated from ab initio potential energy surfaces using transition-state theory (TST). It is concluded that TST with a tunnel factor is valid for reactions of atoms with H/sub 2/ and that curved Arrhenius plots can provide information about the barrier to reaction.

• Research Organization: Dalhousie Univ., Halifax, Nova Scotia
• OSTI ID: 6868796
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:6; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ACTIVATION ENERGY
ARRHENIUS EQUATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DEUTERIUM
ELEMENTS
ENERGY
EQUATIONS
EXPERIMENTAL DATA
FLUIDS
FLUORINE
GASES
HALOGENS
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
KINETICS
LEAST SQUARE FIT
LIGHT NUCLEI
MAXIMUM-LIKELIHOOD FIT
MECHANICS
NONMETALS
NUCLEI
NUMERICAL DATA
NUMERICAL SOLUTION
ODD-ODD NUCLEI
OXYGEN
PARAMETRIC ANALYSIS
PHYSICAL PROPERTIES
POTENTIALS
QUANTUM MECHANICS
REACTION KINETICS
SPECIFIC HEAT
STABLE ISOTOPES
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES