An Electron Spin Resonance Study of Trapped Electrons Formed at 77.5 °k by Gamma Irradiation of an Organic Glass

Radicals formed by y-irradiation of propylene carbonate (PC) glasses at 77 "K were studied by e.s.r. and optical spectroscopy. Trapped electrons were identified by their narrow (AH,,,, = 4.5 G) Gaussian e.s.r. line at g = 2.0028 which was completely resolved from the radical spectrum. The trapped electrons were unstable at 77 OK. They decayed fairly rapidly via a process exhibiting non-homogeneous kinetics believed to be reaction with positive ions. The temperature dependence of the e.s.r. spectra of the other radicals formed is discussed although conclusive assignment of the lines could not be made.Ultraviolet photolysis of the radicals in the irradiated PC glasses produced new species identified as HCO, COT, and CH, by their characteristic e.s.r. spectra. In addition, a complex optical absorption band in the 500-750 nm region was assigned to a combination of the absorption bands of the COT radical anion and the HCO radical.Les radicaux issus de I'irradiation y des verres de carbonate de propylene (CP) a 77 OK, ont tte ttudies par r.p.e. et spectroscopie optique. Les tlectrons pitges ont Ctt identifies en r.p.e. par leur courbe de gausse fine a g = 2.0028 completement resolue a partir du spectre du radical. Leselectrons ainsi pitges sont instables a 77 "K et disparaissent assez rapidement selon un mtcanisme laissant supposer une rtaction avec des ions positifs, d'aprks les cinetiques non homogenes observkes. La variation en fonction de la tempirature du spectrer.p.e. des autres radicaux formtsestdiscutke bien quel'attribution dtfinitivedeces courbes nepuisse Stre faite. La photolyse U.V. des radicaux issus de I'irradiation des verres en CP produit de nouvelles es@ces identifites a HCO, CO; et CH, par leur spectre r.p.e. caracttristique. De plus, une bande d'absorption complexe dans la rtgion de 500 a 750 nm est attribute A une combinaison des bandes d'absorption du radical anion CO; et du radical HCO.

“…The e.s.r. line is normally quite easily powersaturated (8). Photobleaching of the trapped electrons with light in the region corresponding to their optical absorption also occurs (9).…”

Section: Introductionmentioning

confidence: 99%

Trapped Electrons and Radicals in γ-Irradiated Propylene Carbonate Glasses

Shaede¹

1972

“…E X P E R I M E N T A L Techniques of preparation of pure M T H F samples, gamma irradiation, dosimetry, and measurement of e.s.r. spectra have been described (5,6). A linear reproducible magnetic field scan was provided by a…”

Section: Introductionmentioning

confidence: 99%

“…In the series of solutions containing Cl~Hlo, the precision i s poorer, *15%, because the graphical double integrals of spectra having different shapes are being compared. The accuracy depends on the graphical integration and on our calibration of the reference, described earlier (5). Briefly, the concentration of free radicals in the reference sample was determined b y comparison Can.…”

Section: Introductionmentioning

confidence: 99%

Electron Spin Resonance Determination of the Radiolytic Yields of Trapped Electrons and Other Species in an Organic Glass

Smith¹,

Pieroni²

1965

Self Cite

The radiolytic yields, a t liquid nitrogen temperature, of trapped electrons and radicals or radical-ions in 2-methyltetrahydrofuran and the yields of these species plus the biphenyl anion in solutions containing biphenyl have been determined by e.s.r. These measurements were also carried out after photolysis of the trapped electrons. The combined results are interpreted in terms of the identity of the intermediates and the reactions which they undergo. "Dual e.s.r. cavity" techniques have enabled greater accuracy and precision than is nor~nally obtained when concentrations of paramagnetic species are determined by e.s.r.

“…[ l ] applies to inhomogeneously broadened lines. Whilst an important source of broadening is in fact inhomogeneous (the presence of unresolved hyperfine lines), in y-irradiated samples homogeneous contributions are also important (2,10) because of the non-uniform distribution of the electrons. The e.s.r.…”

Section: Discussionmentioning

confidence: 99%

Electron spin resonance studies of radicals condensed from irradiated water vapor: paramagnetic relaxation of trapped electrons in ice

Wardman¹,

Seddon²

1969

The spin-lattice relaxation time T1 of electrons (e,-) trapped in several ice matrices at 77 "K has been estimated to be of the order of s by observation of the electron spin resonance (e.s.r.) dispersion signal under fast passage conditions. These studies, together with measurements of the microwave power saturation of the e.s.r. absorption signal indicate that there is little difference in T1 at 77 "K for e,-in solute-free polycrystalline H,O or D,O ice, y-irradiated 8 M NaOH/H20 or NaOD/D,O glassy ices, and in 8 M NaOD/D,O glasses in which the electrons were produced by photoionization of ferrocyanide ion. This indicates that the predominant spin-lattice relaxation mechanism is not cross relaxation, and that correlations between TI and line width or trap depth are inappropriate.Canadian Journal of Chemistry, 47, 2155Chemistry, 47, (1969 Introduction Electrons trapped in solute-free ice (et-) by condensation of irradiated water vapor appear to have similar chemical properties to those trapped in ice containing high concentrations of electrolytes (1). It was of interest to compare some of the e.s.r. characteristics of e,-in solute-free, polycrystalline ice with those trapped in glassy ice containing high concentrations of solute. The close similarity of the small, negative g-shift for et-in both types of system suggested similar interaction with the matrix via (weak) spin-orbit coupling, and by means of microwave power saturation characteristics we have investigated the interaction of et-with the matrix to see whether any differences could be detected.A study has been published (2) of the saturation characteristics of e,-in y-irradiated glassy ice containing ca. 8 M NaOH or NaOD, and we have, therefore, compared et-in solute-free ice with those in y-irradiated alkaline ice. In the latter case, enhanced spin-spin interaction due to the inhomogeneous spatial distribution of et-could complicate the study, and hence we also compared the saturation behavior of et-produced (presumably homogeneously) by photoionization of a dilute solution of ferrocyanide ion (3) in an identical glassy alkaline ice matrix.