Unimolecular decomposition of the neopentyl radical
- Catholic Univ. of American, Washington, DC (United States)
- National Inst. of Standards and Technology, Gaithersburg, MD (United States)
The kinetics of the unimolecular decomposition of the neopentyl radical has been investigated. Experimentally, the decomposition was monitored in time-resolved experiments by using a heatable tubular reactor coupled to a photoionization mass spectrometer. The radicals were produced indirectly by pulsed excimer laser photolysis of CCl{sub 4} (to produce CCl{sub 3} + Cl) followed by the rapid reaction between the Cl atoms and neopentane to produce neo-C{sub 5}H{sub 11} + HCl. Unimolecular rate constants were determined as a function of bath gas (He, N{sub 2}, and Ar), temperature (10 temperatures between 560 and 650 K), and bath gas density ((3{minus}30) {times} 10{sup 16} molecules cm{sup {minus}3} (He) and (6{minus}12) {times} 10{sup 16} (N{sub 2}, Ar)). The data were fitted within the framework of RRKM theory by using a vibrational model. The high-pressure rate constant in the temperature range studied was determined to be k(neopentyl {yields} isobutene + CH{sub 3}) = 10{sup 13.9 {plus minus} 0.5} exp({minus}30.9 {plus minus} 1.0 kcal mol{sup {minus}1}/RT) s{sup {minus}1}. The average step sizes down for the bath gases used (adjusted parameters in the RRKM calculations) are comparable: 200 (He), 130 (N{sub 2}), and 140 (Ar) cm{sup {minus}1} (all {plus minus} 60 cm{sup {minus}1}). The high-pressure-limit rate constant expression for the reverse reaction, nonterminal addition of CH{sub 3} to isobutene, was obtained from thermochemical calculations by using the results of this study: k(CH{sub 3} + isobutene {yields} neopentyl) = 3.7 {times} 10{sup {minus}13} exp({minus}10.6 kcal mol{sup {minus}1}/RT) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The Arrhenius parameters of this addition reaction indicate that nonterminal addition is inhibited relative to terminal addition mostly by a larger energy barrier to addition, as opposed to possible entropic effects.
- DOE Contract Number:
- FG05-89ER14015
- OSTI ID:
- 7273797
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:20; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400800 -- Combustion
Pyrolysis
& High-Temperature Chemistry
ACTIVATION ENERGY
ALKANES
ARRHENIUS EQUATION
ATOMS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHLORINE
DATA
DATA ANALYSIS
DECOMPOSITION
DENSITY
ELEMENTS
ENERGY
EQUATIONS
EXPERIMENTAL DATA
HALOGENS
HYDROCARBONS
INFORMATION
IONIZATION
KINETICS
MASS SPECTROSCOPY
MATHEMATICAL MODELS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOIONIZATION
PHOTOLYSIS
PHYSICAL PROPERTIES
RADICALS
REACTION KINETICS
RESOLUTION
SPECTROSCOPY
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TIME RESOLUTION
TIMING PROPERTIES