Positive Ion Scavengers Research Articles

Hydrogen Produced by the Hot-Atom-Process in the Radiolysis of Ethane

Abstract The mechanism of the formation of “molecular” hydrogen in the ethane radiolysis at 300 Torr has been studied with ethane-ethane-d6-ethylene mixtures. The G-value of the hydrogen has been found to be 3.3. The addition of electron and positive ion scavengers scarcely affected the formation of the hydrogen at all. From the isotopic composition of the hydrogen, it was demonstrated that most of the hydrogen is formed by molecular detachment from the ethane molecule, while the rest is formed by the abstraction of a hydrogen atom from the ethane molecule by a hot hydrogen atom, the G-value being estimated to be 0.6.

Nanosecond-Pulse Radiolysis of Aniline

The nanosecond-pulse radiolysis of pure aniline reveals two transient species absorbing at 3850 Å and 10 500 Å or higher. Each transient shows a rapid initial first-order decay (t1/2 = 62.5 ± 1.5 nsec) and a long-lived (tens of microseconds) decay. In the presence of electron scavengers, the long-wavelength transient is removed, and yields of the negative ions of biphenyl and pyrene are observed with plateau yields of G = 0.95 ± 0.05. At high concentrations of biphenyl or pyrene, the decay characteristics of the negative ions are identical with those of the species in pure aniline at 3850 Å. Scavenging studies using both positive and negative ion scavengers show that the two transients present in pure aniline are the solvent positive ion (3850 Å) and the solvated electron (10 500 Å) in aniline. The extinction coefficients of φNH2+ and eaniline− determined from ionic scavenging results are 12 050 and 3550 cm2/mole, respectively. The formation of excited states of naphthalene, anthracene, and 1, 2-benzanthracene are observed, and the results clearly show that, where solvent–solute charge-transfer reactions are possible, they lead to the production of ∼20% of the total triplet yields.

Hydrogen Formation in the Radiolysis of Liquid Olefins. The Role of Hot Hydrogen Atoms and Superexcited States

Abstract The γ-radiolysis of liquid olefins was undertaken to obtain reliable evidence for a possible role of hot hydrogen atoms and superexcited states in radiation chemistry. The contribution of thermal hydrogen atoms may reasonably be excluded in this system. The effect of various electron or positive-ion scavengers on hydrogen formation in the radiolyses of liquid propylene and ethylene has been examined. The hydrogen formation is not appreciably affected by these additives, which indicates ionic species may not play an important role in the hydrogen formation. The liquidphase radiolyses of C3H6-C3D6 and C2H4-C2D4 mixtures have also been investigated and compared with those previously reported of C4H8-l - C4D8-l and trans-C4H8 - 2-trans-C4D8-2 mixtures. The data indicate that the hydrogen from the olefins except ethylene may be formed for the most part by bimolecular processes. A large part of the hydrogen from liquid ethylene may be interpreted in terms of the molecular detachment of a hydrogen molecule, while from the other olefins it may be interpreted in terms of the hydrogen-atom abstraction reaction of hot hydrogen atoms formed by direct excitation which must at least partially involve superexcitation. To attempt quantitative substantiation of the above viewpoint a simple calculation has been made based on the so-called optical approximation. Calculated yields of the hydrogen formation are apparently in good agreement with observed ones.

Hydrogen Formation in the Radiolyses of Liquid Butene−1 and trans-Butene−2

The effect of temperature and various electron or positive-ion scavengers on hydrogen formation in the radiolyses of liquid butene−1 and trans-butene−2 have been examined. The hydrogen formation is not appreciably affected by temperature and these additives, which indicates that thermal free radicals and ionic species may not play an important role in hydrogen formation from these olefins. The liquid-phase radiolyses of C4H8−1—C4D8−1 and trans-C4H8−2-trans-C4D8−2 mixtures have also been investigated. The data indicate that hydrogen for the most part may be formed by bimolecular processes. The results have led to the conclusion that the mechanism of the hydrogen formation may be interpreted in terms of the hydrogen-atom abstraction reaction of hot hydrogen atoms or the equivalent formed by the direct excitation which may involve ``superexcitation.''