Complex collision mechanism

Collisions with a Cl-—C-Cl angle of approximately n, with the CH3C1 dipole oriented, do not form the Cl—CH3C1 complex. Collisions oriented in this manner could yield complexes by T — V, but this is an unimportant energy transfer mechanism.38... 

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. 

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. 

A quantitative surface compositional analysis requires the comparison of the experimental yield of the individual clusters with corresponding yields obtained theoretically this may be done by numerical simulation of the complex collision process but the accuracy of the result cannot yet be ascertained. The accuracy of the compositional analysis depends to some extent on such poorly known factors as the interatomic potential, ionization cross-sections and quantum-mechanical corrections to a treatment based on classical trajectories. 

Chemical reactions occurring because of a single kinetic act, i.e., because of a single collision between two molecules, are defined as elementary reactions. More complex laws of dependence on concentrations can be explained by complex reaction mechanisms, i.e., by the idea that most reactions occur as a sequence of many elementary reactions, linked in series or in parallel. As an example, the following... 

These results, obtained on a FT-ICR mass spectrometer, led to the proposal that these reactions proceed through long-lived ion-molecule collision complexes which can undergo secondary reactions within the complex. The mechanism, sketched in Scheme 41, predicts the formation of products originating from attack of F on the neutral by proton transfer, SN2 or elimination reactions. 

According to Equation (5.35), energy transfer by the exchange mechanism is a short-range phenomenon since the exchange term decreases exponentially with the donor-acceptor separation / ao- Since it requires the intervention of an encounter complex (D A) it is also called the overlap or collision mechanism. The Wigner-Witmer spin-selection rules (Section 5.4.1) apply, and the spin-allowed processes... 

There are several interesting features shown by the results which bear discussion. From an examination of Figures 2 to 4 it is evident that the hydrazine yield decreases with increasing discharge power intensity despite a corresponding increase in the decomposition of ammonia. The only reasonable explanation for these results which has been advanced is that hydrazine is formed in the discharge by a complex reaction mechanism and is subsequently decomposed by electron bombardment or other collision phenomena (4, II, 12,13,14). 

If the Langevin formalism is valid, the point to be stressed is that it will apply irrespective of the collision mechanism. Indeed, it has been judged to be valid at the lowest energies for both reactions such as Ar" (D2,D)ArD, which proceeds by a direct mechanism, and CD4, (C )4,CD3)CD5, which proceeds by complex mechanism in this energy range. ... 

One point should be made about the identification of a reflexive separation case in paper [49]. Reflexive separation is defined as an unstable post-collision mechanism that separates the droplets collided at near-head-on impact parameters. In this mechanism, the bulk masses of the colliding droplets remain on the sides of the symmetry plane from where they had approached (therefore reflexive separation). In the case shown in Fig. 7.9, however, which is identified as single reflex separation by Chen and Chen [49], the dyed drop changes its side from above (before collision) to below the symmetry plane (after collision), and the transparent drop moves vice versa. The actual mechanism therefore implies a mutual penetration of the liquid portions in the collided complex, which is not reflexive separation. This mechanism was called crossing separation by Planchette et al. [26] and by Planchette and Brenn [50], since the two liquid portions cross the trajectories of their respective collision partners. 

On the other hand, it is always possible to find a set of stoichiometric equations, each corresponding to a chemical conversion that occurs in the collision of all the reactants covered by the equation. Such a reaction is usually called elementary chemical reaction (or reaction step). If the overall reaction consists of many elementary reactions it is called complex, whereas it is called simple when the overall chemical reaction involves only one elementary step. Identification of all species involved in chemical conversions and determination of the elementary steps correspond to the elucidation of a complex reaction mechanism. 

Although theoretical treatments of ternary association rates are quite successfiil, their success in determining radiative association rates is limited. The key problem is fee calculation of the radiative stabilization rate of fee collision complex. The mechanism by which photons are emitted is uncertain. The few measurements so far undertaken do not give a clear guide. The situation will doubtless be resolved wife both ab initio quantal calculations and a new generation of expoiments including some feat measure the intensity of the radiation emitted in the stabilization process. 

---