Relative collision efficiency

Table I. Relative Collision Efficiencies Estimated from Fitting the Mathematical Model to Experimental Data ...

Fig. 10.15. Relative collision efficiency E / Eq characterising the negative influence of inertial forces K " at different E,-values E =0.01(l), =0.02(2), =0.05(3)...

Whereas c(M)// c(He) values under low-temperature conditions (300—600 K) can be estimated for a given M by means of the relative collision efficiencies in Figures 9—12, the situation is different at high temperatures (shock-wave conditions). Here, relative collision efficiencies including large polyatomic colliders are difficult to measure (thermal instability and shock-wave non-idealities for polyatomic M). Therefore, either experiments with a few inefficient colliders have to be compared with strong-collision (jSc == 1) calculations of Ato from equation (16) ... 

Table 1 Average energies transferred in up and down collisions and average energies dow transferred in down transitions in kJ mol ). Exponential model used for < A > > d.wn relation except for = step-ladder, t = shifted exponential model). Thermal activation, from relative collision efficiencies at 300 K, ref. 63 CHjNC at 554 K, ref. 65 ...

The extraction of information on relative collision efficiencies from measurements of the effect of adding non-reacting gas to the reaction depends upon the applicability of the so-called mixture rule in the simplest case of a unimolecular reaction at its second order limit, this would mean that the total rate of reaction of A in the presence of inert B, C,... would be... 

Plot the curve shown in Figure 5.2 for an infinite sphere and for a 11 sphere, both with 4 X 10 Torr of water vapour present the relative collision efficiency of water is 0.8 on a pressure for pressure basis. 

Because of their third-order behavior, recombination reactions of H, O, and OH (Figs. 10 to 12) are of minor importance in flame propagation at normal or reduced pressure (Fig. 4) but can be relevant at elevated pressure or in ignition or quenching processes because of their chain-terminating character. (The recombination of OH to form H2O2 is discussed below.) Relative collision efficiencies are discussed in Section 1.2. 

On account of their large endothermicity, dissociation reactions of H2,02, or H2O can play a part only in ignition processes at very high temperature in flame propagation they are completely unimportant. Relative collision efficiencies are discussed in Section 1.2. 

Because of the small rate coefficient of H2 H- HO2 H2O2 + H (see below) and the low HO2 concentrations in high-temperature combustion, hydrogen peroxide is mainly formed by OH recombination (Fig. 19), especially at elevated pressure (see Warnatz, 1982). Relative collision efficiencies for third bodies in this reaction are given in Section 1.2. 

The arenium ion/(R)-(— )-2-chlorobutane adducts. A crucial question concerns the chemical identity and the relative spatial arrangement of the components of a microsolvated system, two features of paramount importance to assess the kinetic and the mechanistic role of the corresponding ion-dipole pairs in solution. In the example reported in this section, Cacace and coworkers consider the ion-molecule complexes involved in the classical Friedel-Crafts alkylation of arenes." " At 300 K and under FT-ICR conditions, the benzenium ion CeH reacts with 2-chlorobutane C4H9CI to give the CloHj5 ion with a rate constant of 5 X 10 cm molecule corresponding to a collision efficiency of 2.5% (equations (33) or (34)). ... 

The first quantitative calculation of a high collision efficiency for methyl radical recombination was made by Gorin4 who treated the collision pair as being stabilized by a polarization interaction at relatively large distances. From this point of view the transition state for the reaction corresponds to what might be termed a loose transition state in which there is relatively free libration or rotation of the two methyls relative to each other. 

Figure 5. The variation of relative colloid stability, expressed as collision efficiency factor, with A1(III) dosage as compared with colloid surface coverage from adsorption of Al(lll)...

Colloid Stability as a Function of pH, Ct, and S. The effects of pertinent solution variables (pH, Al(III) dosage Ct, Al(III) dosage relative to surface area concentration of the dispersed phase S upon the collision efficiency, have been determined experimentally for silica dispersions and hydrolyzed Al(III). However, one cannot draw any conclusion from the experimental results with respect to the direct relationship between conditions in the solution phase and those on the colloid surface. It has been indicated by Sommerauer, Sussman, and Stumm (17) that large concentration gradients may exist at the solid solution interface which could lead to reactions that are not predictable from known solution parameters. 

Figure 7 gives the relative stability of Si02 colloids in terms of the observed collision efficiency as a function of Al(III) dosage Ct for different pH values. Such data can be used to define quantitatively similar log Ct-pH domains of coagulation and restabilization, expressed as the critical concentrations of beginning destabilization and complete restabilization (c.c.c. and c.s.c.) as given by Matijevic et al. (8, 9, 10). A similar procedure for the determination of the c.c.c. and c.s.c. concentration limits has been proposed by Teot (22). 

Figure 9. Relative effects of collision efficiency factor and velocity gradient on...

For the He/MeONO system, the temperature dependence of Pn for He was determined [119. An 18% decrease in over a 31 K increase in temperature was observed. This trend is similar to that observed previously for MIC [122] and can be explained by considering the size of the vibrational partition function of MeONO which increases by 19% over the 31 K temperature interval studied. Previous studies of collisional energy transfer in MeONO have shown that the vibrational degrees of freedom of the colliders is important. Thus, an inert gas such as helium, which has only translational degrees of freedom, would be expected to show a decrease in collision efficiency relative to MeONO on itself with increasing temperature. 

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