Spectator model

The results that are obtained from the TOF curves are compared to three models, namely a Franck-Condon model, a spectator model, and a quasi-oscillator model. It is concluded that the quasi-oscillator model has the right kind of qualitative potential to explain the results. This quasi-oscillator potential has a series of quasi-minima, about which the Rqq oscillates while Rq3 gradually increases. 

The fj that appears in the atomic fragments (X) is large, and suggests that an impulsive model for dissociation is the correct theoretical interpretation of the results. In fact, the spectator model appears to predict the fj that are observed. 

Schematic picture of the participant-spectator model. The hot participant region is formed from nucleons in the target-projectile overlap region. The target and projectile remnants on the periphery act as spectators, which then decay statistically...

What would be the opposite situation to the spectator model It would be the case where the final momentum of the C product is predominantly determined by the momentum imparted from the BC bond breaking. An example of this situation would be that of a rebound of A, meaning a purely repulsive reaction. In this case, there is a strong contribution to p from the repulsive energy release of the BC breaking. 

Table 1 summarizes the results for the reaction of several different states with H or Cl atoms. The results for the states in the region of three quanta of excitation follow the simple spectator model. The first column in the table reports the eightfold difference in reactivity of the I02>" and the l03> states with H atoms and also shows that adding two quanta of bend makes the I02> I2> state about twice as reactive as the I02> state but almost four times less reactive than the nearly isoenergetic I03> state. The reactivities of the Cl atom shown in the second column show a similar pattern for these same states. The state with bending excitation is... 

It is easy to realize that this spectator model can account for the observation that very little of the reaction exoergicity is released as translational energy of the products. The Cl atom approaches the HI molecule with a particular momentum and captures the H. But the H atom is so light that the momentum of the 1 atom is left nearly unchanged, and so too is that of the Cl atom, which is part of the HCl product. But if energy is to be conserved without altering the translational motion, it follows that the exoergicity of the reaction mnst be deposited in the internal motion of the HCl. The quantitative version of our conclusion is the subject of Problem B. Here we proceed to look for additional experimental evidence that can lend support to the model. 

The spectator model makes a statement about vectors, namely that not only the magnitude but also the direction of the momentum of the iodine atom is unchanged in the colhsion (Newton s second law requires a force to change the direction of the momentum). Hence, the product iodine atom should appear in the same direction as that of the incident HI while the product HCl will appear in the direction of the incident chlorine atom. Leaving the details for later, it is sufficient to say that this description, which we colorfully call the spectator stripping picture, is quahtatively the behavior found experimentally. The product HCl appears mainly in the forward direction (i.e., in the direction of the incident chlorine atom). Note again that such a statement is only possible because we are focusing our attention on the isolated collision. In the bulk, the products would soon collide with other molecules and very rapidly lose all memory of their nascent direction of motion. 

Vestal ML, Wahrhaftig AL and Futrell JH (1976) Application of a modified elastic spectator model to proton transfer reactions in polyatomic system. Journal of Physical Chemistry, 80 2892-2899. 

According to the ideal stripping model, the incident X + ion collides with a quasi-free H atom while the other H atom in the H2 molecule merely participates as idle spectator to the reaction. The conservation of momentum in the system X +-H requires the secondary ion XH + to be formed with the velocity ... 

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

One attempt to remedy the limitations of the 2D model, and yet retain its simplicity, is the so-called hole model [25] which represents a simple static way to average over this distribution of barriers. If the variation of barrier height with these spectator variables is given as (X, Y, i), ), then the 6D dissociation probability S6D is approximated in terms of the 2D S2D as... 

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