Exit channel, potential energy

A summary of work in fluorine chemistry as determined from crossed molecular beam studies of reaction dynamics Is presented. Special emphasis is given to studies of unimolecular decay of long-lived complexes formed from bimolecular association of fluorine atoms with unsaturated hydrocarbons. The experimental results are discussed in terms of statistical models for energy randomization in the complex as well as the role of the exit channel potential energy barrier in determining the product translational energy distribution. 

These plots show several important features. The AE i. distributions of the five type A surfaces are nearly identical this illustrates the insensitivity of the relative translational energy distributions to the HCC bend to HC stretch coupling. The same is true for the two type B surfaces. The AE distributions for the type A and B surfaces are quite broad and each has an average value greater than the exit-channel potential energy release i,e., 3.5 and 0.5 kcal/mol for the type A and B surfaces, respectively. 

Figure 1.5. Femtosecond spectroscopy of bimolecular collisions. The cartoon shown in (a illustrates how pump and probe pulses initiate and monitor the progress of H + COj->[HO. .. CO]->OH + CO collisions. The huild-up of OH product is recorded via the intensity of fluorescence excited hy the prohe laser as a function of pump-prohe time delay, as presented in (h). Potential energy curves governing the collision between excited Na atoms and Hj are given in (c) these show how the Na + H collision can proceed along two possible exit channels, leading either to formation of NaH + H or to Na + H by collisional energy exchange.

Figure 4. Schematic potential energy surface for the reaction of FeO" " with methane. The sohd line indicates the sextet surface the quartet surface is shown with a dotted line, in each case leading to the production of Fe + CH3OH. The dashed line leads to formation of FeOET + CH3. The pathway leading to the minor FeCH2" + H2O channel is not shown. Schematic structures are shown for the three minima the [OFe CHJ entrance channel complex, [HO—Fe—CH3] insertion intermediate, and Fe" (CH30H) exit channel complex. See text for details on the calculations on which the potential energy surface is based.

The prototype potential surface invoked in chemical kinetics is a two-dimensional surface with a saddle equilibrium point and two exit channels at lower energies. The classical and quantal dynamics of such surfaces has been the object of many studies since the pioneering works by Wigner and Polanyi. Recent advances in nonlinear dynamical systems theory have provided powerful tools, such as the concepts of bifurcations and chaos, to investigate the classical dynamics from a new point of view and to perform the semiclassical... 

D. M. Neumark We indeed take the translational energy distribution from CH3O dissociation to be evidence for exit channel interactions on a repulsive potential-energy surface. This is in contrast to photodissociation of the vinoxy radical, for which very little variation of the CH3 + CO translational energy distribution occurs over a 0.5-eV range of excitation energy. 

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