Halide ion capture by radicals. Electron spin resonance spectra of R ₃ P·—hal and R ₂ S·—hal σ * radicals

Exposure of methanolic or acidic aqueous glasses containing halide salts together with organic phosphines or sulphides gave the electron loss centres R3P˙+ or R2S˙+ which reacted with halide ions (hal–) to give the σ* radicals R3P·—hal and R2S·—hal which were identified by e.s.r. spectroscopy. These were formed in competition with the σ* dimer radicals R3P·—PR3+ and R2S·—SR2+, also detected by e.s.r. spectroscopy. Interconversion between these species on annealing the glasses above 77 K is discussed. These reactions are significant in being the reverse of dissociative electron capture. Also, they constitute a method of converting an electron-loss centre into an electron excess centre.