Collision geometry

Figure A3.1.9. Hard sphere collision geometry in the plane of the collision. Here a is the diameter of the spheres.

One of the few theoretical papers trying to explain acceleration under the action of microwaves has recently been published by A. Miklavc [18]. He stated that large increases in the rates of chemical reactions occur because of the effects of rotational excitation on collision geometry. This could be cautiously considered when one has knowledge of the quasi-nil energy involved by microwave interaction according to Planck s law [E = hc/X = 0.3 cal/mol]. 

Reacting particles must collide with the proper orientation relative to one another. This is also known as having the correct collision geometry. The importance of proper collision geometry can be illustrated by the following reaction. 

Figure 6.9 shows five of the many possible ways in which NO and NO3 can collide. Only one of these five possibilities has the correct collision geometry for a reaction to occur. As shown in the figure, only a certain orientation of reactants prior to collision leads to the formation of two molecules of nitrogen dioxide. 

Go to the Chemistry 12 Electronic Learning Partner to learn more about collision geometry. 

STRONG ACCELERATION OF CHEMICAL REACTIONS ARISING THROUGH THE EFFECTS OF ROTATIONAL EXCITATION OF REAGENTS ON COLLISION GEOMETRY... 

Strong acceleration of chemical reactions arising through the effects of rotational excitation of reagents on collision geometry... 

The efficiency of agglomeration, Pa, depends on the supersaturation, collision geometry, and details of the flow (83-85), namely. Pa increases with increases in the supersaturation ratio S and decreases with increasing rate of energy dissipation e. 

We have studied the reaction dynamics of the collision Nag+ + Na for a fixed collision geometry (with impact parameter 6=0) but in a wide range of impact energies Ecm. In Fig. 1, the total kinetic energy loss (tkel) AE =Eem -Ecm(t -> +oo), with Ecm(t +oo) the final kinetic energy of the relative motion between cluster-projectile and atomic target in the centre-of-mass system is shown for Ecm = 0.2 eV... 1 MeV. 

Figure 1 tkel of relative motion AE in central Nag+ + Na collisions for a fixed collision geometry (insert) as a function of the center-of-mass impact energy Ecm calculated with na-qmd (solid line) and qmd (dotted line). Vibrational and electronic contributions to A E are distinguished by grey and light-grey shaded areas, respectively. 

Figure 2 Difference of the impact energy and the actual kinetic energy AE(t) of relative motion (left column) and displacement d(t) of the cluster atoms (right) as a function of time t for selected impact energies Ecm and the same collision geometry as in Fig. 1, calculated with na-qmd (dark solid lines). In the left column, the corresponding adiabatic qmd calculations (dotted lines) are also shown for comparison.

Strong Acceleration of Chemical Reactions Arising Through the Effects of Rotational Excitation on Collision Geometry Miller W.H. 

Calculations have shown that the faster diffusion rates might be explained by an increase in the factor A with no change in activation energy. Miklavc [39], by analyzing the rotational dependence of the reaction 0 + HC1 0H- -Cl, concluded that marked acceleration may occur as a result of the effects of rotational excitation on collision geometry. 

FIGURE 1.21 Scheme of parameters defining the ion-molecule collision geometry (a) orientation angles of the ion with respect to three orthogonal axes and (h) the impact parameter b for a gas molecule (grey) with velocity v scattering on the ion (unshaded), solid circle is the center of mass of the system. 

Figure 11.12 I Geometric factors can also be important in determining whether a molecular collision is reactive. For the oxygen atom to react with N2O, it must strike the oxygen end of the molecule. The importance of collision geometry depends on the shapes of the molecules in the reaction.

Although collision theory has provided considerable insight beyond simple hard spheres, it cannot properly address questions such as what fraction of collision geometries are likely to lead to reaction. Such issues cannot be... 

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