Energy Effects in Ion-Molecule Reactions

The effect of internal (vibrational) energy upon reaction rate is also one that is not well studied in single mass spectrometer sources with ions formed by electron impact. A considerable number of reaction rate constants have been measured over quite a range of electron energies with essentially 

Of considerably greater significance is the work of Friedman and co-workers on reactions of helium and neon with hydrogen. They have established that the reaction of H2 in the ground vibrational state with either helium or neon would be endothermic by several kcal mole However, some reaction is observed and more careful examination of the process shows that reaction with helium becomes quite rapid for hydrogen ion in the fifth or greater vibrational level and with neon for H2 in the second or higher vibrational level. 

Of considerable interest, also, is the observation by Munson that butyl ions formed from n-butane and /so-butane differ greatly in their reactivity with propylene, 1-pentene, and 2,2,4-trimethylpentane. The C4H9 from n-butane (presumably 2-C4H9 ) is much more reactive and evidently does not rearrange to the tertiary structure in times of about 10 sec. 

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