The photolysis of neohyphen;C5H12mdash;neohyphen;C5D12mixtures has been investigated at 1470 and 1236 Aring;. From the products formed in the absence and presence of NO or H2S, the occurrence of the following fragmentation processes could be derived:neominus;C5H12*rarr;CH4plus;isominus;C4H8CH3plus;Hplus;isominus;C4H8CH3plus;CH3plus;C3H6.These modes of decomposition also prevail when neopentane is excited by collision with electrons accelerated by an electrical field applied during radiolysis. At 1236 Aring;, the relative probabilities of occurrence of Processes (1), (2), and (3) are approximately 1.0, 4.5, and 1.1.From the isotopic analysis of the products formed in the direct and inerthyphen;gashyphen;sensitized radiolysis of neohyphen;C5H12mdash;neohyphen;C5D12mixtures in the presence of NO, O2, or I2as freehyphen;radical scavengers, it could be derived that the fragment ions C2H3+, C2H5+, C3H5+, and C3H7+are formed and undergo hydridehyphen;ion transfer reactions with neopentane to form C2H4, C2H6, C3H6, and C3H8, respectively. Assuming that this is the only mode of reaction of these ions in the system, ionhyphen;pair yields of 0.028, 0.068, 0.062, and 0.015 are obtained for the above listed ions at a pressure of 30 Torr.The propyl ion, which has a secondary propyl structure, undergoes a hydride transfer reaction with neopentane at a rate which is slower by more than one order of magnitude than the analogous reactions of the ethyl or allyl ions. It is observed that this relatively slow ionmdash;molecule reaction is inhibited when an electric field is applied to the system, probably because of the collection of propyl ions on the cathode. In agreement with masshyphen;spectrometric results, it is suggested that propyl ions are formed mainly as a result of the decomposition of the C5H11+ion which is formed in the hydridehyphen;ion transfer processes.The C4H9+ion does not react with neopentane but does, under certain conditions, yield isobutene by an unspecified process. The ionhyphen;pair yield of isobutene increases with increasing pressure and with diminishing recombination energy of added inert gas.In the direct radiolysis, the ionhyphen;pair yields of the fragment ions formed with appearance potentials above that of C4H9+are seen to diminish when the pressure is increased, while, in the inerthyphen;gashyphen;sensitized radiolysis, most of these ions increase with an increase of the recombination energy of the inerthyphen;gas ions, Xe+, Kr+, Ar+, Ne+.
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