The e.p.r. spectrum of thiyl radicals is obtained when dilute solutions of aliphatic mercaptans are photolyzed in a xenon matrix at 77 OK. No proton hyperfine structure is observed at low concentrations of thiol but it appears at higher concentrations due to the reaction of hot hydrogen atoms with solute mercaptan molecules. When small amounts of the thiols are dissolved in glassy hydrocarbon matrices such as 3-methylpentane, there is produced after photolysis hyperfine structure characteristic of the solvent as well as the thiyl resonance. The e.s.r. absorption due to the solvent species disappears when the matrix is warmed a few degrees above 77 "K but thiyl radicals are stable up to the melting point of the glass. The corresponding y-irradiated glasses do not give thiyl absorption, but two other species are produced along with solvent radicals. No thiyl radicals are observed following radiolysis, or upon photobleaching the new species. The spatial distribution of the neutral radicals in the glasses is discussed in view of these results.Le spectre de r.p.e. de radicaux thiyl est obtenu lors de la photolyse de solutions dilukes de mercaptans aliphatiques dans une matrice de xenon a 77 OK. On n'observe pas la structure hyperfine du proton en utilisant de faibles concentrations de thiol, mais elle apparait lorsqu'on utilise des concentrations plus ClevCes a cause de la reaction des atomes d'hydrogkne chauds avec les molCcules de mercaptan en solution. Si on dissout de petites quantites de thiol dans des matrices d'hydrocarbure vitreuses, tel le methylpentane-3, il se produit apres photolyse, une structure hyperfine qui est caracteristique du solvant aussi bien que de la resonance du thiyl. L'absorption r.p.e. due a l'espece solvant disparait quand la matrice est chauffee a quelques degris au-dessus de 77 OK, mais les radicaux thiyl demeurent stables jusqu'au point de fusion du verre. Les verres irradits aux rayons-y ne donnent pas d'absorption thiyl, mais deux autres especes sont produites en meme temps que les radicaux de solvant. On n'observe pas de radicaux thiyl apres radiolyse, ou pendant la photodCcoloration des nouvelles espkces. On discute de la distribution spatiale des radicaux neutres dans les verres pour arriver aces rksultats.
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