Velocity distribution product recoil

The angular distributions of the 0(3P2) fragments show the degree of correlation between the product recoil velocity (v) with the electric vector of the dissociating light and are typically characterized by the lab frame anisotropy parameter (/ ) given in the equation,52,53... 

We focus our attention on the DIPR (direct interaction with product repulsion) model and its variant, the DIPR-DIP model, mainly because it can be used to predict an entire range of dynamic observables in chemical reactions angular and recoil velocity distributions, rotational energy and orientation and vibrational energy of the reaction products. It is also able to account for the switch from the rebound to the stripping reaction mechanism for a given system when the collision energy is increased. The beauty of the model is its ability to include semiempirical parameters, each of which is related to a different physical phenomenon. 

Shortly after these results were published, Bernstein and coworkers (10,11) completed a crossed beam study of the reaction of K atoms with HBr and DBr, with velocity selection of the incident K-atom beam and velocity analysis of the KBr product. Analysis of the data showed that the product KBr c.m. angular distributions are broadly backward-peaked for K + HBr and nearly isotropic for K + DBr and that the recoil velocity distributions are broad and extend to the maximum value allowed energetically. These results differ considerably from the results for K + TBr since (i) when taken together, the angular distributions imply that the KBr product shifts nonmonotonically from broadly backward-peaked to nearly isotropic to sharply backward-peaked with the isotopic substitutions HBr DBr TBr and (ii) the mean recoil energy is much lower (and therefore the product excitation much higher) for K + TBr. These differences are still unresolved at this writing. 

Measurement of product velocity distributions was not feasible in the D + H2 study however, even in experiments where the recoil velocity. distribution is accurately measured, it is diflBcult to extract a c.m. cross section due to the diflBculty of estimating a resolution that depends on beam shapes, detector geometry, and electron density gradients in the ionizer. 

For the analysis of the secondary reaction channels, the forward convolution technique is also used, but with additional averaging over the velocities of the fragmenting products of the primary reaction channel [11], Here, the decomposing species are no longer traveling in a well-collimated molecular beam with a narrow velocity distribution. On the contrary, these species have recoiled from the molecular beam in all directions with velocity distributions defined by the primary decomposition. 

Not only the product angular distribution can be determined, but also its recoil velocities. This type of measurement, i.e. both the angular and velocity distribution of the reaction products, is currently made using the universal crossed-beam technique in which a rotatable electron-impact mass spectrometer is used... 

Early studies included diffusion flames [6-7] and extensive work on molecular beams measuring total and differential react )n cross-sections from elastic [8] and reactive scattering experiments [9-10]. Among the many measurements that have been carried out one may mention product angular and recoil velocity distributions... 

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