Effect of vibrational excitation in neutral reactants

The effect of vibrational excitation in the neutral reactant was first studied with the exothermic reaction 

A plausible explanation for these experimental facts has been developed by Kaufman and Koski [215] which was later verified by Pipano and Kaufman [216] and is based on the constructed potential energy curves of N2 0. According to these, and N2 combine along the repulsive curve of N2 0 which does not cross the curve corresponding to the products. The reactants first cross by a change of multiplicity to the 7T, ground state of N2 0 , and thence, by another change of multiplicity, to the S repulsive state which correlates to NO ( S )+ N( S), viz. 

The low probability of this reaction ( 1 reaction per 10 collisions) is then attributed to the spin forbidden nature of the N2 0 formation step. This reaction would require a significant amount of activation energy, but Kaufman and Koski have pointed out the possible lowering of the crossover point between the 2 and the curves owing to the attractive polarization force between O and N2.  

When the kinetic energy of or the vibrational energy of N2 is increased, the lowest quartet state of N2 0 becomes energetically accessible and the reaction proceeds via this state. The transition to this state is not spin forbidden and a much greater probability for the reaction is expected. 

The effect of the vibrational excitation of N2 on the cross-section or rate coefficient of reaction (127) has also been studied in the interaction energy ranges between 2.5—64 eV (ref. 217) and 0.05—15 eV (ref. 218) 

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