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ELECTRON-SPIN EXCHANGE-REACTIONS OF MUONIUM ATOMS WITH CHROMIUM(III) COMPLEXES - CONTRASTS WITH POSITRONIUM

TitleELECTRON-SPIN EXCHANGE-REACTIONS OF MUONIUM ATOMS WITH CHROMIUM(III) COMPLEXES - CONTRASTS WITH POSITRONIUM
Publication TypeJournal Article
Year of Publication1994
AuthorsLazzarini, E, Stadlbauer, JM, Venkateswaran, K, Gillis, HA, Porter, GB, Walker, DC
JournalJournal of Physical Chemistry
Volume98
Pagination8050-8052
Date PublishedAug
Type of ArticleArticle
ISBN Number0022-3654
Keywordsradicals, RADIOLYSIS, relaxation
Abstract

Muonium atoms were observed to undergo a fast reaction with several chromium(III) complexes in water, with rate constants in the neighborhood of 10(10) M(-1) s(-1). The reaction occurring is attributed to a simple electron-spin-exchange in muonium, catalyzed by the paramagnetic d(3) metal ions. There is a quantum mechanical statistical factor for this process of 62% per collision, which becomes 50% when multicollisional cage effects in solution are included, with the result that the observed rates are close to the diffusion-controlled limit for a muonium reaction in water. The implication is that nearly half of the encounters between muonium and a Cr complex result in electron spin exchange. These muonium rates are faster by a factor of similar to 5 than the corresponding reactions of positronium. They also show a different dependence on the nature of the ligands. These differences are attributed to positronium being larger and more polarizable than muonium, so that spin-spin coupling with the metal’s d electrons is weaker and more sensitive to the nephelauxetic effect of the ligands in the case of positronium. The corresponding reactions involving ordinary H atoms are not available for comparison but presumably resemble muonium’s.

URL<Go to ISI>://A1994PC61900022