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Ab initio predictions and experimental confirmation of large tunneling contributions to rate constants and kinetic isotope effects for hydrogen-atom transfer reactions

Technical Report ·
OSTI ID:6807574
; ; ; ;
The importance of tunneling in gas-phase hydrogen-atom transfer reactions is investigated. New experimental measurements and theoretical calculations are presented for the intramolecular kinetic isotope effect K/sub 3/K/sub 4/. This new information and earlier results for the reaction rate constants for the O + H/sub 2/ and O + D/sub 2/ reactions provide strong evidence for the dominance of tunneling in all four reactions at temperatures below 500K. Three theoretical approaches are used: the improved canonical variational theory with classical reaction coordinate motion (ICVT), ICVT with least-action ground-state transmission coefficients to account for tunneling (ICVT/LAG), and the reduced-dimensionally quantum calculations with an adiabatic incorporation of bending motion (denoted more specifically as collinear exact quantum with ground-state bend or CEQB/G). All calculations use an accurate ab initio potential energy surface. In general the agreement is good between the ICVT/LAG and CEQB/G calculations and the experimental results. Although the ICVT results (which neglect tunneling effects) are accurate at high temperatures (1400-1900K), they are inconsistent with the experimental results temperatures (318-500K) indicating that tunneling is important. The LAG method also provides a measure of the importance of tunneling for this reaction: the percentage of the reaction that occurs by tunneling. For the O + H/sub 2/ reaction, this factor is 94% and 76% at 300 and 400K, respectively.
Research Organization:
Chemical Dynamics Corp., Upper Marlboro, MD (USA)
OSTI ID:
6807574
Report Number(s):
AD-A-175628/7/XAB
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
640304 -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ATOMS
CHEMICAL REACTIONS
COLLISIONS
COORDINATES
DEUTERIUM
ELEMENTS
ENERGY
HIGH TEMPERATURE
HYDROGEN
HYDROGEN ISOTOPES
HYDROGEN TRANSFER
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
MOLECULE COLLISIONS
MOTION
NONMETALS
NUCLEI
ODD-ODD NUCLEI
OXIDATION
OXYGEN
POTENTIAL ENERGY
REACTION KINETICS
STABLE ISOTOPES
SURFACES
TUNNELING
VERY HIGH TEMPERATURE