Role of the Low-Energy Excited States in the Radiolysis of Aromatic Liquids

Abstract

The contribution of the low-energy excited states to the overall product formation in the radiolysis of simple aromatic liquids--benzene, pyridine, toluene, and aniline--has been examined by comparison of product yields obtained in UV-photolysis and in γ-radiolysis. In photolysis, these electronic excited states were selectively populated using UV-light excitation sources with various energies. Yields of molecular hydrogen and of "dimers" (biphenyl, bibenzyl, dipyridyl for benzene, toluene, pyridine, respectively, and of ammonia and diphenylamine for aniline) have been determined, since they are the most abundant radiolytic products. Negligibly small production of molecular hydrogen in the UV-photolysis of aromatic liquids with excitation to energies of 4.88, 5.41, 5.79, and 6.70 eV and the lack of a scavenger effect suggest that this product originates from short-lived high-energy singlet states. A significant reduction in "dimer" radiation-chemical yields in the presence of scavengers such as anthracene or naphthalene indicates that the triplet excited states are important precursors to these products. The results for toluene and aniline suggest that efficient dissociation from the lowest-energy excited triplet state leads to noticeable "dimer" production. For benzene and pyridine, the lowest-energy triplet excited states are not likely to fragment into radicals because of the relatively large energy gap between the excited state level and corresponding bond dissociation energy. The "dimer" formation in the radiolysis of benzene and pyridine is likely to involve short-lived high-energy triplet states.

Gamma and heavy ion radiolysis of ionic liquids: A comparative study

“…[55] The exact mechanism for the decay of aromatic compounds is still uncertain, but excited states formed by the neutralization reaction then decay to the ground state with little molecular decomposition. [56] An interesting situation arises when a molecule contains both an aromatic component and an aliphatic one. For instance, the addition of a methyl group to benzene to give toluene results in a slightly higher yield of H 2 .…”

“…For instance, the addition of a methyl group to benzene to give toluene results in a slightly higher yield of H 2 . [56] ILs are expected to be synthesized and used with a wide combination of aromatic and aliphatic components so an understanding of their different contributions to final products is useful for determination of their overall usefulness and stability.…”

Growth of polyphenyls via ion–molecule reactions: An experimental and theoretical mechanistic study

“…Moving from Titan's atmosphere down to Earth, biphenyl and larger polyphenyls -in addition to PAHs and carbonaceous dust particles [14,15] -have been detected in the plasma treatment of gaseous mixtures containing benzene [16,17] as well as in the radiolysis of liquid [18,19,20] and gaseous benzene [21]. In Ref.…”

Irradiated benzene ice provides clues to meteoritic organic chemistry

“…When radical scavengers are added to benzene before irradiation, to react with the Å C 6 H 5 radicals produced, some biphenyl formation is still observed. Excited states of benzene or the benzene radical cation may play a role, but in both cases details remain to be determined (Baidak et al, 2011).…”