Inhibition of Ps Formation in Benzene and Cyclohexane by CH3CI and CH3Br: Correlation to Radiation Chemistry Results

G. Wikander, O. E. Mogensen, Niels Jørgen Pedersen

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Positron-annihilation lifetime spectra have been measured for mixtures of CH3Cl and CH3Br in cyclohexane and of CH3Cl in benzene. The ortho-positronium (Ps) yield decreased monotonically from 38% and 43% in cyclohexane and benzene respectively to 11% in pure CH3Cl and 6% in pure CH3Br. The strength of the inhibition of Ps formation by CH3Br was ten times that of CH3Cl in cyclohexane, because the CH3Br− anion debrominates rapidly, while CH3Cl− is long-lived (= 30 ns) compared to the maximum time of Ps formation of 400–500 ps. as shown in radiation chemistry. The positron can pick off the electron from the CH3X− anions to form Ps. while it forms a bound state with the halides. X−. CH3Cl was a roughly three times weaker Ps inhibitor in benzene than in cyclohexane, which shows that CH3Cl− does not dechlorinate in times comparable to or shorter than 400–500 ps in benzene. An improved model for the explanation of Ps formation in mixtures, where the Ps yield versus electron scavenger concentration has a minimum, is proposed and discussed.
    Original languageEnglish
    JournalChemical Physics
    Volume77
    Issue number2
    Pages (from-to)159-168
    ISSN0301-0104
    Publication statusPublished - 1983

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