Bimodal product energy distribution

Microscopic branching refers to the observation of a bimodal product energy distribution from one reaction channel (HX) and a normal product energy distribution from the other reaction channel. It appears that the bimodal distribution occurs for the product, HX, containing the most electronegative atom. Figure 9 shows the triangle plots for the detailed vibrational state distributions for the HBr and HC1 products from H + BrCl. Bimodality is seen in the HC1 distribution. The HBr distribution from H + BrCl closely resembles the HBr distribution from H + Br2 and results from a direct reaction with the Br end of BrCl. 

Bimodal rotational energy distributions have been observed [267] for the HCl product from the reaction H + SQ2, indicative of the existence of both a direct and migratory mechanism as was observed in the reactions of H atoms with interhalogen molecules [see Sect. 3.1.1(c)]. The internal energy disposal was determined to be = 0.42 and >... 

Both processes can produce unimodal and bimodal molecular weight distributions. Currently, bimodal MWDs may have to be produced in dual reactor systems. They are energy intensive and require more capital and increase the control complexity. Some licensors claim now to achieve similar product quality with a single reactor by using a dual site catalyst with bimodal capability. 

Pressure effect on the product distribution in supercritical media would resolve the problem. If the reaction proceeds via the competitive concerted/ stepwise mechanism, the reaction under a higher pressure is expected to give more exo isomer because the activation volume is considered to be smaller for concerted process than the stepwise one and hence more concerted reaction is expected under a higher pressure. If, on the other hand, bimodal lifetime distribution of trajectories is the origin of the stereoselection, the product ratio is expected to approach to unity under high-pressure conditions, since energy randomization is more effective under a high pressure. 

Energy disposal has been studied for the reactions F + IC1 [553] and I2 [554, 555] using laser-induced fluorescence detection of the IF product. For F + IC1, the results indicate a direct reaction with the IF vibrational product distribution being inverted with a peak at v — 7. As with the Cl and Br atom reactions, the majority of the reaction energy appears as IF internal energy ( 0.14). For F + I2, the IF product vibrational state distribution appears to be bimodal [554] with peak at v = 0 and a secondary peak at v = 18 with the distribution extending up to the limit imposed by the reaction exoergicity. Trajectory... 

The TOP distribution is bimodal for thin deposition. The low-energy component appeared only for thin-deposited CI2. It contains information on the Cl atoms photoproduced on the substrate surface by laser irradiation. Cl atoms photogenerated on the substrate surface are decelerated by strong interaction between these atoms and the surface. A part of Cl atoms may result in the generation of etching products ... 

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