Collision mechanism

Obviously, experiments designed to measure cross-sections as a function of energy are needed. At present, tandem experiments are not capable of high precision at low energies because one must assume details of collision mechanics and because it is difficult to estimate collection efficiencies in forward scattering geometry (15). The extension of all known techniques to lower energy (64, 65) and the further development of pulse methods (58) offer the possibility for advances in this area. 

Table II. Kinematic Conditions for the Formation of Tertiary Ions by Various Collision Mechanisms...

Relation between Velocities of Primary Collision Mechanism and Secondary Ions... 

Typical results for these three collision mechanisms are shown in Figure 3 where the relative intensities of the primary, secondary, and tertiary ions are plotted against N, the concentration of molecules in the source. In deriving these curves, the parameters used were kp = 2.0 X 10 9 cc./molecule-sec. k8 = 1.0 X 10 9 cc./molecule-sec. tp = 8.5 X 10 7 sec., (the residence time of the ion (jn/e — 33) in a field of strength 9.1 volts/cm. in the Leeds mass spectrometer). In applying this analysis to a system in which the tertiary ion reacts to form quaternary and higher order ions, ITtotal represents the sum of tertiaries, quaternaries, etc. 

It was ewn that, for the interaction of H with Ni(110) and (111), dissociative adsorption occiors via a direct collision mechanism. A small activation barrierexists only for Ni(111)/H. Ihe sticking is do-... 

The model as formulated in this section cannot be used to predict a priori the solids entrainment rate into the jet because of the two empirical constants in Eq. (61). Lefroy and Davidson (1969) have developed a theoretical model based on a particle collision mechanism for entrainment of solid particles into a jet. The resulting equation for particle entrainment velocity is... 

It should be noted, however, that gaining a deeper insight into the problem of ionization phenomena is not the only reason for steady interest in the problem. Data on charged particle impact ionization is used both for industrial applications and for fundamental scientific research. For applications it is the collisions rates and total cross sections which are usually the most relevant. But in studies focused on the understanding of collision mechanisms of ionization processes, most of the information is lost in the total cross sections due to the integration over the momenta of the ejected electrons in the exit channel. Therefore it is the singly and doubly differential cross sections which are of... 

Energy transfer occurs in a long-lived collision complex. An exited molecule is often very polarizable and may form a collision complex with the Q molecule in the ground state. The collision complex A Q has a longer lifetime than the corresponding AQ collision complex. The formation of an exciplex provides the energy transfer by a collision mechanism. 

In Table 1 (pp. 251-254), IM rate constants for reaction systems that have been measured at both atmospheric pressure and in the HP or LP range are listed. Also provided are the expected IM collision rate constants calculated from either Langevin or ADO theory. (Note that the rate constants of several IM reactions that have been studied at atmospheric pressure" are not included in Table I because these systems have not been studied in the LP or HP ranges.) In general, it is noted that pressure-related differences in these data sets are not usually large. Where significant differences are noted, the suspected causes have been previously discussed in Section IIB. These include the reactions of Hcj and Ne with NO , for which pressure-enhanced reaction rates have been attributed to the onset of a termolecular collision mechanism at atmospheric pressure and the reactions of Atj with NO and Cl with CHjBr , for which pressure-enhanced rate constants have been attributed to the approach of the high-pressure limit of kinetic behavior for these reaction systems. 

The reaction of the proposed intermediate in the nonsticky collision mechanism proceeds very rapidly with hydroxide—when it doesn t have to substitute very fast. And in fact, in competition experiments that Olcott and I did with hydroxide and all the other possible reactants in solution, hydroxide was 100% efficient in capturing the aquo complex intermediate. 

The most satisfactory explanation is that the rate is increased beyond the maximum rate of activation by collision through the operation of a chain mechanism. The observations of Sprenger on the peculiar behaviour of nitrogen pentoxide at low pressures suggest strongly that chains are propagated. Moreover, if the rate of the azoisopropane reaction at the lowest pressures should prove to be greater than can be accounted for on the basis of the simple collision mechanism, a chain mechanism can be assumed without difficulty since the reaction is quite markedly exothermic. 

In the case of homogeneous interaction the mechanism of collisions between separate drops will show some resemblance to the collision mechanism between separate molecules, as assumed in the kinetic gas theory. In accordance with this theory, the collision rate po can be put equal to... 

V. COLLISION MECHANISMS AND THEORETICAL IMPLICATIONS A. General Effects of Internal Excitation... 

According to the different collision mechanisms in these modes, a distinction between them can be made with the help of the Knudsen number K which compares the mean-free-path length A of the particles with a characteristic dimension d of the tube ... 

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