Orientation-dependent reaction cross-section

An Application of the RSMM. The RSMM was first applied to reactions for which the j-dependence of cross sections is dominated by the "orientational" effect. For example, the model proved to be very useful to rationalize the striking structure of the theoretical a(j) for Li + HF found by Noorbatcha and Sathyamurthy mentioned earlier [21]. Here, we will illustrate the RSMM in an application to the system 0( P) + HQ -> OH + Q [24]. For this reaction two LEPS PES s exist both equjdly qualified to explain temperature dependencies of experimentally known rate constants. 

Experiments showed that the cross section of the reaction a(N) substantially depends on the light polarization and, hence, on the orientation of the molecule HF( 1, 2). These specific features of the behavior of the dependence of a N) on the translational energy of the reactants and polarization of the exciting light are related to anisotropy of the interaction of the reactants, which results in the dependence of the potential barrier on the collision angle of the reactants. Therefore, the reaction cross section is determined by the geometry of collision. 

In addition to energy disposal and angular distributions, simulation of the M + CH3I reaction must explain the dependence of the reaction cross section upon (118,281-283) upon orientation of i.e., the... 

In summary, preliminary experiments have demonstrated that the efficiency and outcome of electron ionization is influenced by molecular orientation. That is, the magnitude of the electron impact ionization cross section depends on the spatial orientation of the molecule widi respect to the electron projectile. The ionization efficiency is lowest for electron impact on the negative end of the molecular dipole. In addition, the mass spectrum is orientation-dependent for example, in the ionization of CH3CI the ratio CHjCriCHj depends on the molecular orientation. There are both similarities in and differences between the effect of orientation on electron transfer (as an elementary step in the harpoon mechanism) and electron impact ionization, but there is a substantial effect in both cases. It seems likely that other types of particle interactions, for example, free-radical chemistry and ion-molecule chemistry, may also exhibit a dependence on relative spatial orientation. The information emerging from these studies should contribute one more perspective to our view of particle interactions and eventually to a deeper understanding of complex chemical and biological reaction mechanisms. 

Since the value of A depends on the value chosen for the cross-section, and the values are base on taking the values for non-reactive collision cross section. Hence, orientation requirement can be taken into account by replacing the collision cross section a2 in equation (2.50) by the reactive cross section o 2. A more conventional procedure takes the view that the cross section for reaction can be expressed in terms of the collisional cross section and stearic factor P such that a 2. 

In 5.1, we describe how the lOSA is used to calculate photodissociation cross sections. Particular care has to be taken in averaging over the orientation-angle dependent scattering wavefunction using the bending wavefunction of the ground state. To do this we apply, to the reaction problem, a procedure developed by Segev and Shapiro for the vibrational predissociation of Van der Waals complexes [ 51]. Then in 5.2, we present our calculations of the photoabsorption spectrum for the H2O photodissociation (VII). 

In summary, the utility of micro-SERS spectroscopy for the evaluation of potential-dependent interfacial com-petititve and displacement reactions at chargwl surface has been demonstrated. The data obtained allow the determination of the chemical identity, structure, orientation, competitive and displacement adsorption of cationic surfactants and nitrophenol in the first adsorption layer. The examples of these measurements in the field of surfactants and organic pollutants reviewed in this article were selected to illustrate the sensitivity, molecular specificity of adsorption processes, accuracy, ease of substrate preparation, and manifold applications of Raman analysis. The spatial resolution of the laser microprobe, coupled with the 10 enhancement of the Raman cross-section, means that picogram quantities of material localized to pm-sized surfaces areas can be detected and identified by SERS vibrational spectroscopy. 

Figure 3.11 Orientation dependence of the cross-section for the reaction H + D2(v= /= 0) HD + D at the two indicated values of the collision energy Ej- The ordinate is dff R/dcos y = 2ctr(cos y). The solid curves were calculated from the angle-dependent line-of-centers model, Eq. (3.34), and the (open and filled) points represent dynamical computations (these are quasi-classical trajectory results that have statistical error bars as discussed in Chapter 5) on the ab initio potential surface referred to in Figure 3.10 [adapted from N. C. Blais, R. B. Bernstein, and R. D. Levine, J. Phys. Chem. 89, 20 (1985)].

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