Collision contour maps

Fig. 21. The product D-atom velocity-flux contour map, d

Fig. 7. Velocity contour maps for D2+ from the reaction D+(HD, H)Dj at 5-5 eV collision energy (a)experimental measurements (f>) theoretical results.26...

Fig.9. Contour maps for KrD for the reaction Kr+(D2, D)KrD+ at 089 eV and 2-70eV centre of mass collision energies.42...

Fig. 8. Two-dimensional exchange spectroscopy (often called 2D-ELDOR) of the spin-labeled 3K-8 peptide with mixing time T = 296 nsec. Both the 2D surface and the contour map are shown. The peaks along the diagonal are related to the absorption spectrum of the spin label. The high-held M,= - line is weak because of experimental dead time artifacts. The cross-peaks, especially those between the outermost hyperfine lines, provide direct evidence of Heisenberg spin exchange. The cross-peak intensity can be used to determine the second-order rate constant for collisions between peptides.

In the two systems discussed thus far, the product scattering is very anisotropic. This indicates the lifetime of a molecular collision is very short relative to rotation of the complex formed between reactants (i.e., < --10" sec). If this were not the case, the scattering of product would be symmetric about the center of mass since all information about initial geometry of the collision would be lost after a few rotations. In fact, long-lived complexes have been observed in many cases. For example, the flux (velocity-angle) contour map for CsF formed in the reaction... 

Fig. 6-10 Flux velocity-angle contour map for DF obtained from the reaction F + D2 DF + D. The initial relative translational energy was 1.68 kcal/mole. The circles represent the largest possible value of the final velocity of DF consistent with the vibrational quantum number v. [Adapted from Y. T. Lee, in Physics of Electronic and Atomic Collisions, VII ICPEAC 1971, Fig. 4a. Reproduced by permission of copyright owner, North-Holland Publishing Co., Amsterdam.]...

The ultimate desirable outcome in any chemical reaction dynamic experiment is the measurement of flux-velocity contour maps for quantum-state-selected products from photofragmentation, or inelastic and reactive collisions processes for which the initial state is also well defined. From such contour maps, complete information on the chemical process can be deduced in favourable cases. 

Figure 20.8 Contour maps of different PESs. Top non-reactive atom-diatom potential. Bottom reactive potential showing the presence of a potential well that may facilitate theformation of a collision complex...

Contour maps for the angle-velocity flux of ArD+ produced in this reaction have been computed on the basis of a highly approximate potential-energy surface. The model treats Ar+ as a hard sphere and Dg as a pair of hard spheres nearly in contact. The relative motion prior to Ar -Da collision is governed by the ion-induced-dipole potential between Ar+ and D2. During collision the ion and each atom are treated as hard spheres. An ArD+ ion is presumed to have formed if the relative translational energy of the nuclei is less than the bond dissociation energy. As the products... 

Figure 3. Upper panel DF angular distributions at 0.80 kcal/mol and 1.68 kcal/tnol collision energy. Lower panel Cartesian flux contour maps generated from these data.

Figure 5.12. (a) Potential energy diagrams and contour maps for a head-on collision between an atom A and a molecule BC which is initially in the ground state. The trajectory in (b) corresponds to a process in which translational energy of A has been converted to vibrational energy of molecule BC. 

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