Products angular distribution

As presaged by Lee and co-workers,57 it is in the angular distributions that the clearest sign of resonance behavior is observed. In Fig. 13, we plot the calculated DCS versus Ec and 9 for F + Fp (p) — HF (v = 2) + H summed over j -states. Near the resonance energy, we observe a very dramatic change in the angular product distribution. At Ec = 0.34kcal/mol... 

In summary, the H + HD reaction shows little sign of resonance scattering in the ICS. Furthermore, the product distributions without angle resolution show no unusual behavior as functions of energy that might indicate resonance behavior. On the other hand, the forward peaking in the angular product distribution does appear to reveal resonance structure. Since time-delay analysis is at present not possible in a molecular beam experiment, it is the combination of a sharp forward peak with the unusual... 

The classical description is quite different from the quantum. In classical dynamics we describe the coordinates and momenta simultaneously as a function of time and can follow the path of the system as it goes from reactants to products during the collision. These paths, called trajectories, provide a fnotion picture of collision process. The results of any real collision can be represented by computing a large number of trajectories to obtain distribution of post-collisions properties of interest (e.g. energy or angular distribution). In fact, the trajectory calculation means the transformation of one distribution function (reagent distribution, pre-collision) into another (product distribution, post-collision), which is determined by PE function. 

The photodissociation process takes place most frequently at excitation of the molecule to a non-bonded state, with subsequent dissociation into products. Since the angular part of the transition probability, according to Chapter 2, is still dependent on the mutual orientation of the E-vector of the initiating light beam and on the transition dipole moment d, one may expect spatial anisotropy of angular momenta distribution both in the dissociation products and in the set of molecules which remains undestroyed. 

Model calculations usually divide the reaction into two parts and make various assumptions about the nature of the entrance channel (or reactant) and exit channel (or product) interactions. In some models, these interactions are treated independently and in others some degree of coupling is introduced. Not all reaction models are capable of describing the nature of the product energy disposal many are concerned only with the total reaction cross section or the product angular scattering distributions. 

Figure 8.8 Angular regions that lead to the different products. The regions are weighted by (1/2) J cos 6d6 to predict the product distributions. Source Adapted with permission from Doubleday, C. Suhrada, C. R Houk, K. N. J. Am. Chem. Soc. 2006,128, 90. Copyright 2006 American Chemical Society.

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