Effects of molecular structure and temperature on the tunneling abstraction of D from C-D bonds by trapped H and D atoms in alkane glasses at 5-29 K
The rates of the tunneling abstraction of D atoms from the C-D bonds of three alkane glasses at 5 to 29/sup 0/K by trapped H or D atoms increase in the sequence 3-methylpentane-d/sub 14/ < 3-methylheptane-d/sub 18/ < methylcyclohexane-d/sub 14/. This parallels both the increasing density of the matrices and the increasing proportion of secondary + tertiary C-D bonds to primary C-D bonds. The apparent activation energy (E/sub A/) is < 100 cal mol/sup -1/ in every case. For H/sub tr/ it shows a unique reversal in sign, being positive from 18 to 29/sup 0/K, zero from 10 to 18/sup 0/K, and negative from 5 to 10/sup 0/K. For D/sub tr/ it decreases below 18/sup 0/K but does not pass through a minimum. The temperature region of the discontinuities of E/sub A/ is that in which both stabilization of van der Waals molecules of the type H.C/sub 6/H/sub 14/ and quenching of the torsional vibrations of the CD/sub 3/ groups are to be expected. The ratios of the rates of decay of H/sub tr/ to D/sub tr/, R(H/sub tr/)/R(D/sub tr/), are all 2.1 to 0.8 in 3MP-d/sub 14/ and 3MHp-d/sub 18/ at 5 to 29/sup 0/K, but range from 30 at 5/sup 0/K to 3 at 29/sup 0/K in MCHx. 4 figures, 1 table.
- Research Organization:
- Univ. of Wisconsin, Madison
- OSTI ID:
- 5675581
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 83:20; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400302 -- Organic Chemistry-- Isotope Effects-- (-1987)
400500* -- Photochemistry
ACTIVATION ENERGY
ALKANES
CHEMICAL REACTIONS
CRYOGENIC FLUIDS
CYCLOALKANES
CYCLOHEXANE
DECOMPOSITION
DEUTERIUM
DEUTERIUM COMPOUNDS
ELEMENTS
ENERGY
FLUIDS
GLASS
HALOGEN COMPOUNDS
HYDRIODIC ACID
HYDROCARBONS
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INORGANIC ACIDS
IODINE COMPOUNDS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MOLECULAR STRUCTURE
NONMETALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
STABLE ISOTOPES
TEMPERATURE EFFECTS
TUNNELING
ULTRALOW TEMPERATURE
VERY LOW TEMPERATURE