Pressure, rate constants for

The effect of a pressure of 80 and 150 MPa on the spin-state transition has been also studied [169], a series of spectra obtained at 150 MPa being shown in Fig. 32. The speetra show relaxation effects as line broadening and linewidth asymmetry. Calculated spectra were obtained in the same way as at ambient pressure. Rate constants for a number of temperatures are listed in Table 12, the parameter values resulting from an Arrhenius plot of the rate constants being listed in Table 13. In Fig. 33, the quantity 5g of Eq. (36) has been plotted as a... 

Recently, some additional low-pressure rate constants for the syn-anti process in MeONO have been obtained [770]. Figure 5 shows pressure-dependent rate constants (k/k J for syne anti exchange in pure MeONO at 262.2 K. The solid line corresponds to RRKM calculated values using E0 = 49.8 kJ mol-1 and a = 5.4 A. 

Figure 2. Plot of the high-pressure rate constant for CH3 recombination versus reciprocal temperature. Theoretical results are presented as solid curves 1 through 4 and are discussed in the text (1) generalized RRKM with a = 0.8 A-1 (2) generalized RRKM with a = 1 A-1 (3) generalized RRKM with a — 1 A-1 and an approximate symmetry correction (4) a simplified SACM treatment. The open circles are the experimental results of Ref. 33.

The PES calculated at the G2M (CC2)//PW91PW91/6-311-i-G(3df) level is shown in Fig. 11. The key structures of species involved in this reaction are shown in Fig. 12. TSl is the transition state for the OCIO ClOO isomerization reaction with a barrier of 63.3 kcal/mol, whereas TS2 is that for the CIO O C10 0 isomerization with a barrier of 61.5 kcal/mol. Predicted rate constants for the production of O + CIO and Cl + O2 resulted directly from the unimolecular decomposition processes with no contributions from the isomerization reactions. Comparison of the predicted ClOO decomposition rate with experimentally available values is shown in Fig. 13. The low- and high-pressure rate constants for OCIO and ClOO dissociations can be expressed by ... 

The low- and high-pressure rate constants for the association process can be expressed by ... 

As shown in Fig. 11, O + CIO can directly form OCIO and ClOO intermediates, the latter dissociates to Cl + O2. The isomerization from OCIO to ClOO needs a very high barrier, 63.3 kcal/mol it is not crucial to the measured kinetics of these reactions. The comparison of the total rate constants with experimental data is shown in Fig. 27. The results show that O + CIO -> Cl + 02 channel is pressure independent and dominant formation of OCIO is pressure dependent and has some contribution to the total rate constants at lower temperatures and higher pressures as shown in the figure. The low- and high- pressure rate constants for the reactions. 

In addition, we also calculated the reverse rate constants of reaction (11 b), forming stabilized ClOO by collisional deactivation the results are in reasonable agreement with experimental values as shown in Fig. 28. The low- and high- pressure rate constants for this process can be expressed as ... 

Limiting high pressure rate constants for > C2 alkyl peroxy radicals are identical to that for the C2H502- radical k = 9 x 10 12 cm3 molecule-1 s-1, independent of temperature over the range 250 to 350 K. 

Table II. Summary of Calculated and Experimental High-Pressure Rate Constants for C2F6 Bath Gas...

Unimolecular dissociation and isomerization reactions of chemically activated and stabilized adduct resulting from addition or combination reactions are analyzed by constructing potential energy diagrams. Some high-pressure rate constants for each channel are obtained from literature or referenced estimation techniques. Kinetics parameters for uni-molecular and bimolecular (chemical activation) reactions are then calculated using multifrequency QRRK analysis iork(E) [199, 200, 63]. 

By considering the limiting case of high pressure, we again find that the high-pressure rate constant for stabilization is independent of [M]. More interesting is to examine the pressure dependence of the apparent rate constant for the C + D product channel. This rate constant at its high-pressure limit is inversely proportional to pressure. This is also true for the redissociation reaction, which is just a special product channel. 

In this derivation the rate constant k presents the temperature-dependent high-pressure rate constant for the addition reaction and the function h E) is used (as before) to calculate the energy distribution of the initial complex AB(E). 

A look at the equations (110) 113) clarifies this conclusion the apparent high-pressure rate constant for stabilization of A is obviously pressure independent and the high-pressure rate constant for product formation from A is inversely proportional to [M] (due to This is reasonable because product formation competes with collisional stabilization. The high-pressure stabilization rate constant for B formation ( stab,B) also depends inversely on [M] for the same reason and thus its dependence of [M] differs from Arstab hy [M] The same [M] difference is observed between AprodA and Apr dB, since latter high-pressure rate constant shows a quadratic inverse dependence on [M]. 

The high pressure rate constants for a large number of radical-radical association reactions have been studied theoretically by Klippenstein, Harding, Miller and co-workers.They have focused especially, but not exclusively, on the recombination of alkyl radicals, such as CH3 -I- CHs, of resonance-stabilised radicals such as C3H3 + CsHs, and of the association of H atoms with alkyl and aryl radicals such as CH3 + H and CgHs -I- H. These reactions are particularly important in high temperature systems and experimental information about their rate constants is limited, generally to room temperature and above. 

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