The reactions of the acetone and acetyl cation with acetone have been investigated in a photoionization mass spectrometer. Reaction of the acetone cation with <tex-math>$\leq 0.3\ {\rm eV}$</tex-math> internal energy occurs essentially at every collision <tex-math>$(k=8.4\times 10^{-10}\ {\rm ml}/\text{molecule}\ {\rm sec})$</tex-math>, but decreases slightly with an increase in internal energy. Two reaction channels are observed for the acetone cation: (a) <tex-math>${\rm CH}_{3}{\rm COCH}_{3}{}^{+}+{\rm CH}_{3}{\rm COCH}_{3}\rightarrow ({\rm CH}_{3})_{2}{\rm COH}^{+}+{\rm CH}_{3}{\rm COCH}_{2}$</tex-math> and (b) <tex-math>${\rm CH}_{3}{\rm COCH}_{3}{}^{+}+{\rm CH}_{3}{\rm COCH}_{3}\rightarrow {\rm CH}_{3}{\rm COCH}_{3}{\rm COCH}_{3}{}^{+}+{\rm CH}_{3}$</tex-math>. The <tex-math>${\rm CH}_{3}{\rm CO}^{+}$</tex-math> ion reacts mainly as follows: <tex-math>${\rm CH}_{3}{\rm CO}^{+}+{\rm CH}_{3}{\rm COCH}_{3}\rightarrow {\rm CH}_{3}\cdot {\rm COCH}_{3}{\rm COCH}_{3}{}^{+}\ (k\cong 4.6\times 10^{-10}\ {\rm ml}/\text{molecule}\ {\rm sec})$</tex-math>. At pressures above <tex-math>$10^{-3}\ \text{Torr}\ ({\rm CH}_{3})_{2}{\rm COH}^{+}$</tex-math> and <tex-math>${\rm CH}_{3}{\rm COCH}_{3}{\rm COCH}_{3}{}^{+}$</tex-math> reacts further with acetone to produce <tex-math>$({\rm CH}_{3}{\rm COCH}_{3})_{n}{\rm H}^{+}$</tex-math>. It is suggested that in liquid phase radiolysis experiments the acetone cation will react within <tex-math>$10^{-12}-10^{-13}\ {\rm sec}$</tex-math>. Recent radiolysis experiments in which acetone was used as a solvent are discussed in the light of this premise.

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