Unimolecular dissociation of cyclohexene at extremely high temperatures: behavior of the energy-transfer collision efficiency
The dissociation of cyclehexene has been observed in shock waves with the laser schlieren and pulsed laser flash absorption techniques over 1200-2000 K and 110-550 Torr, using 2% and 4% cyclohexene in krypton and 0.2% cyclohexene in argon. The inverse Diels-Alder molecular elimination to 1,3-butadiene and ethylene is clearly the dominant dissociation channel under all conditions. Rate constants derived for this reaction have a high precision, with rms deviations of only a few percent. Unimolecular falloff, although slight at the lowest temperatures, is clearly discernible for all temperatures. A simple RRKM calculation, using a nonspecific vibration model transition state, is fit to the measured rate constants, giving log k/sub infinity/ = 15.57 - 65.7 (kcal/mol)/2.303RT with a barrier of 61.9 kcal/mol. These RRKM calculations were performed with the energy-transfer collision efficiency derived from both fixed <..delta..E>/sub down/ and <..delta..E>/sub all/. A good fit is achieved with either below 1500 K, but above this a fixed <..delta..E>/sub down/ gives rates which are much too small, and this deficiency cannot be compensated by other changes, whereas a fixed <..delta..E>/sub all/ provides quite satisfactory agreement with the measurements for all conditions. This situation is similar to that indicated by other large molecule dissociations at extreme temperatures.
- Research Organization:
- Univ. of Illinois, Chicago
- DOE Contract Number:
- AC02-78ER04759
- OSTI ID:
- 6420900
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:11; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
400500 -- Photochemistry
ALKENES
BUTADIENE
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CYCLOALKENES
DATA
DIELS-ALDER REACTION
DIENES
DISSOCIATION
ETHYLENE
EXPERIMENTAL DATA
HEATING
HEXENES
HYDROCARBONS
INFORMATION
KINETICS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
PLASMA HEATING
POLYENES
PRODUCTION
REACTION KINETICS
SHOCK HEATING
SHOCK TUBES
STRUCTURAL CHEMICAL ANALYSIS
THERMODYNAMIC PROPERTIES
VERY HIGH TEMPERATURE