Hot hydrogen atom--hydrocarbon reactions. Dependence of yields on structure and energy
The hot atom reactions of H atoms with C/sub 2/D/sub 6/, C/sub 3/D/sub 8/ , an d n-C/sub 4/D/sub 10/, and D atoms with C/sub 2/H/sub 6/, CH/sub 8/, n-C/sub 4/H/sub 10/, and n-C/sub 6 /H/sub 14/ have been studied over the hot atom initial energy range 1.1-2.9 eV, using HBr and DBr as photochemical sources. The steady- state treatment provides a consistent description of the data, giving ratios of the hot atom rate coefficients k/sub R//k/sub T/, k/sub R//k/sub t/, and k/su b M/ /k/sub t/, where k/sub R/ is the hydrocarbon reaction coefficient, k/sub M/ the hydrocarbon moderation coefficient, k/sub t/ the hydrogen halide total interaction coefficient, and k/sub T/ = k/sub R/ + k/sub M/. The integral reaction probabili ty k/sub R//k/sub T/ is found to increase monotonically with energy for all systems, and increases strongly with n for the C/sub n/ compounds studied. k/sub R//k/sub t/ has a similar dependence on hydrocarbon structure, and a similar dependence on energy for the DBr-RH systems, but is nearly energy independent for the HBr-RD systems. k/sub M//k/sub t/ shows more variable behavior than the two k/sub R/ functions, but is approximately the same for different C/sub n/, compounds, and in general decreases about 50% for HBr--RD and 20% for DRr-RH from 1.1 to 2.9 eV, with an increase at intermediate energies for the DBr--RH systems. At 2.9 eV the k/sub M//k/sub t/ values are within 0.8 plus or minus 0.1 for HBr--RD and 1.2 plus or minus 0.1 for DBr-RH. The k/sub R//k/ sub t/ values increase at this energy by half the C/sub 2/ value with each increase in n, and (k/sub R//k/sub t/)/sub DBr-RH/ = 4.8(k/sub R//k/sub t/)/sub HBr-RD/. For HBr at 2.9 eV and HI at 185 nm (3.3 -3.6 eV), (k/sub t/)HI/(k/sub t/ )/sub HBr/ is only weakly dependent on the RD compound, with values in the range 1.7- 2.0 from the k/sub R//k/sub t/ data and 1.8 - 2.1 from the k/sub M//k/sub t/ data. An average per bond yield formula ls found to fit the integral reaction probability data in the 2 -- 3 eV region, giving a secondary to primary bond yield ratio, Y/sub s//Y/sub P/, of 2.4- 2.6 for the C/sub 2/--C/sub 4/ cases. Th e composite isotope effect, (k/sub R//k/sub T/)/sub D-RH//(k/sub R//k/sub T/)/sub H-RD/, is within 2.2 plus or minus 0.3 for the C/sub 2/-C/sub 4/ hydrocarbons for initial hot atom energies of 1.1, 1.6, and 2.9 eV, and is consistent with the effect expected from inertial considerations. In general, it appears that the relalive hot alom reaction yields in different RH compounds or RD compounds are primarily due to reactive effects rather than moderation effects (i.e., to large differences in the primary and secondary bond reactivities). (auth)
- Research Organization:
- Univ. of California, Santa Barbara
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-29-024062
- OSTI ID:
- 4338469
- Journal Information:
- J. Phys. Chem., v. 78, no. 6, pp. 559-567, Other Information: Orig. Receipt Date: 30-JUN-74
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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N40220 -Chemistry-Inorganic
Organic
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*HEXANE- HOT ATOM CHEMISTRY
*HYDROGEN- HOT ATOM CHEMISTRY
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CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
DEUTERIUM COMPOUNDS
ENERGY