The formic acid molecule is used as a model for a computational comparison of the Willi-Wolfsberg curvature parameter (K) method (Type K calculations) and the Johnston-Bonner-Wilson method (Type II calculations), both including bond order (N) and barrier curvature (ν1‡ ≠ 0) effects, for calculation of 13C kinetic isotope effects involving reaction coordinate eigenvectors consisting nominally of two nonzero elements. Results obtained by the two methods cover similar ranges of value of calculated k12C/k13C. Reaction coordinate eigenvectors (uncontaminated for Type II results) may involve as much as 20% extraneous displacement in Type K results when ν1‡ ≅ 800 i cm−1; however, the effect on (ν1‡/ν′1‡), the temperature independent factor (TIF) in k12C/k13C, is so small as to be of limited practical significance. The remainder (TDF) of the isotopic rate constant ratio for various combinations of K and N (Type K) or of ν1‡ and N (Type II) can be arranged well into magnitude sequence by invocation of details of the input F and G matrices in the first order high temperature approximation. But, Type K and Type II results similar only with respect to barrier curvature (as indicated by value of ν1‡) may be very different. The Type K approach (at least for two-element reaction coordinates) seems the more serviceable for data matching and may be conceptually the simpler. The Type II approach, however, seems the more instructive concerning the influence of specific internal coordinate displacements on values of the kinetic isotope effect.
Intennolecular and intramolecular I3C kinetic isotope effects in the pyrolysis of dimethyl ether were measured at temperatures between 451 and 5S0·C; initial pressures were between 14 and 1000 torr. A few experiments on the NO-inhibited reaction were carried out at SOI·C. Both isotope effects are of the order of 1 % and decrease with increasing temperature; the temperature dependence of the intermolecular effect is the greater. No significant pressure effects were observed. The isotope effects arise in the destruction of the symmetry of the reactant in hydrogen transfer reactions of the form R +C 2 H30C! H3->RH+C2 H 2 0C! H 3 , where R"CH 3 , H, or NO. The method of three-element reaction coordinates was used to model the hydrogen transfer, the elements being displacements in the stretching coordinates R···H, H-··C2, and C 2 :.: O. With adjustments of the transition state diagonal force field which are physically and chemically reasonable, the best simultaneous fit to the experimental results is obtained for reaction coordinates in which displacements in R···H and H"'C 2 are large but that in C 2 " 0 is small. The fit is not critically sensitive to the degree of transfer of H from C2 to R in the range 25%-75%, and in that range is essentially the same for R=H, CH 3 , or NO. Predictions are made of kHlko for comparative pyrolyses of CH 3 0CH 3 and CD 3 0CD 3 .
Coated particle waste forms have been developed as part of the multibarrier concept at Pacific Northwest laboratory (PNl) under the Alternative Waste Forms Program for the Department of Energy (DOE). Battelle Columbus laboratory (BCl), under subcontract to PNl, was assigned the task of coating simulated nuclear waste glass marbles and ceramic pellets with low-temperature pyrolytic carbon (IT-PyC) using the chemical vapor deposition (CVD) process. This effort at BCl was a continuation of previous subcontracts from PNl to develop high temperature PyC, A1 2 0 3 and SiC, CVD coatings for ceramic nuclear waste forms. The development of IT-PyC coatings as described in this report was initiated to reduce the release of volatile waste form components and to permit the coating of larger glass marbles that have low temperature softening points (550 to 600°C). Fluidized bed coaters for smaller particles «2mm) and newly developed screw-agitated coaters for larger particles (>2mm) were used.Coating temperatures were reduced from >1000°C for conventional CVD high temperature PyC to -500°C by using a catalyst. The coating gas combination that produced the highest quality coatings was found to be Ni(CO)4 as the catalyst, C 2 H 2 as the carbon source gas, and H2 as a diluent. Carbon deposition was found to be temperature dependent with a maximum rate observed at 530°C. Coating rates were typically 6 to 7 pm/hour. The screw-agitated coater approach to coating large-diameter particles was demonstrated to be feasible. Clearances are important between the auger walls and coater to eliminate binding and attrition. Coatings prepared in fluidized bed coaters using similar parameters are better in quality and are deposited at two to three times the rate as in screw-agitated coaters. v • " ACKNOWLEDGMENTS
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