Pulse Radiolysis of Neopentane in the Gas Phase

The pulse radiolysis of gaseous neopentane has been investigated in the absence and presence of electron scavengers (SF₆, CD₃I, CCl₄). Deuterium labeling experiments show that the stable product molecules can be accounted for by (a) radical combination reactions involving mainly CH₃ and H; (b) hydride ion transfer reactions involving C₂H₃ ⁺, C₂H₅ ⁺, and C₃H₅ ⁺; (c) neutralization reactions of C₄H₉ ⁺ and C₅H₁₁ ⁺; and (d) unimolecular dissociation of the parent ion (C₅H₁₂ ⁺) and of electronically excited neopentane. Neutralization of the t-C₄H₉ ⁺ ion, which is the major positive ion in the system occurs as follows: (a) t-C₄H₉ ⁺ + e → i-C₄H₈ + H and (b) t-C₄H₉ ⁺ + e → 2CH₃ + C₃H₆. It is shown that C₅H₁₁ ⁺ produced in hydride ion transfer reaction C H ⁺ + neo-C₅H₁₂ → C H + C₅H₁₁ ⁺ (where C H ⁺ = C₂H₃ ⁺, C₂H₅ ⁺, and C₃H₅ ⁺) rearranges to the CH₃C⁺(CH₃)CH₂CH₃ structure prior to neutralization. A detailed accounting of all products produced in the unimolecular and bimolecular reactions led to the conclusion that the ratio of neutral electronically excited molecules to parent ions (N_ex/N₊) is 0.28.