Angular distribution resonance scattering

At the time the experiments were perfomied (1984), this discrepancy between theory and experiment was attributed to quantum mechanical resonances drat led to enhanced reaction probability in the FlF(u = 3) chaimel for high impact parameter collisions. Flowever, since 1984, several new potential energy surfaces using a combination of ab initio calculations and empirical corrections were developed in which the bend potential near the barrier was found to be very flat or even non-collinear [49, M], in contrast to the Muckennan V surface. In 1988, Sato [ ] showed that classical trajectory calculations on a surface with a bent transition-state geometry produced angular distributions in which the FIF(u = 3) product was peaked at 0 = 0°, while the FIF(u = 2) product was predominantly scattered into the backward hemisphere (0 > 90°), thereby qualitatively reproducing the most important features in figure A3.7.5. 

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... 

PAD (perturbed angular distribution) is a variation of PAC with nuclear excitation by a particle beam from an accelerator. QMS is quasielastic MdBbauer-spectroscopy, QNS is quasielastic neutron spectroscopy. For MOBbauer spectroscopy (MS), perturbed angular correlation (PAC), and /J-nuclear magnetic resonance (/3-NMR), the accessible SE jump frequencies are determined by the life time (rN) of the nuclear states involved in the spectroscopic process. Since NMR is a resonance method, the resonance frequency of the experiment sets the time window. With neutron scattering, the time window is determined by the possible energy resolution of the spectrometer as explained later. 

Several reasons have been put forward to explain the change in the angular intensity pattern of the photoelectrons. One explanation is that intermediate neutral energy levels are ac-Stark shifted into resonance and contribute new selection rules to the photoionization process [53,54], Another possibility is that the electrons of the Kr or D2 are driven into the core Kr+ or D2 in a scattering-like process that creates interference fringes in the photoelectron angular distribution due to interference between multiple scattering channels [55],... 

In this paper, we will present a detailed analysis of the way In which resonances may affect the angular distribution of the products of reactive collisions. To do this, we have used an approximate three-dimensional (3D) quantum theory of reactive scattering (the Bending-Corrected Rotating Linear Model, or BCRLM) to generate the detailed scattering Information (S matrices) needed to compute the angular distribution of reaction products. We also employ a variety of tools, notably lifetime matrix analysis, to characterize the Importance of a resonance mechanism to the dynamics of reactions. 

As a result, we hope to gain Insight Into how the resonant component of the scattering mechanism Is manifested In the angular distribution of reaction products. Applications of these techniques to two reactive systems, F+H2 and He+H2 > will be reviewed. 

The study of quantum effects such as resonances In atom-molecule reactions has been largely confined to coupled-channel calculations for collisions constrained to colllnear geometries. Progress In quantum reactive scattering techniques Is reviewed periodically (1-4). A few 3D quantum calculations of simple reactions, some more approximate (5-17) than others (18-19), have been concerned with resonance features In the reaction dynamics, and with the Increasing sophistication and sensitivity of molecular beam experiments (20-23), It has become evident that the angular distribution of reaction products Is likely to be the most sensitive observable manifestation of resonant contributions to reaction mechanisms. 

The effect of resonances on angular distributions In reactive scattering can be effectively modeled If one can successfully separate the multichannel S matrix Into Its background and resonant components (33,36), so that (In matrix form). 

The scattering of neutrons by Be is accompanied, at the 2.6 MeV resonance, by a peak in the (na) reaction. Assignments of spin are based partly on angular distribution measurements. 

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