Atom-Transfer Reactions Translational Excitation

Integral reaction probabilities have been determined for numerous reactions of photochemically generated hot H or D atoms. The experiments of Kuppermann and White/ on the reaction 

Studies have been made of the reactions of hot H or D with several alkanes. However, only the experiments on 

X It is interesting to note that this technique is not applicable to H or D atoms, where there is greatest opportunity for successful photochemical experiments. 

Reaction kcal/mole kcal/mole kcal/mole Dynamics function Reference 

Among the reactions listed in Table 1.1 are those of K atoms with Bra, CH3I, and CsF  

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Metastable oxygen ions 02(a ITu) react fast with atoms or molecules (Ar, N2, CO, H2) in reactions that are endothermic with ground-state oxygen ions the respective rate constants do not depend much on translational energy. An interesting case is the charge-transfer reaction of electronically excited NO+(a S" ) with Ar The reaction is endothermic by 0.09 eV, and its rate constant increases with translational energy from the thermal value of 3 x 10 " cm s to a value of about 9 x 10 cm s at 3 eV in a way typical of... 

Quantitative analyses of the energetics of the neutral reaction products were not performed. However, our ion retarding potential analyses indicate some energy transfer from translational to internal modes, mainly vibrational excitation. At collision energies >4.5 eV, these reactions could also produce neutral atomic products. 

The importance of photosensitization derives f rom the f act that reaction is produced in the presence of the sensitizer in circumstances where the direct photochemical dissociation is not possible. The example just cited is a case in point. Radiation of wavelength 253.7 nm was absorbed by a mercury atom. The excited mercury atom dissociated a molecule of hydrogen by transferring the excitation energy in a collision. The mercury atom had 471.5 kJ of this 432.0 kJ were needed for the dissociation 39.5 kJ are left over and go into additional translational energy of the two hydrogen atoms and the mercury atom. If the attempt is made to dissociate H2 directly by the process... 

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