Detection of trapped electrons in organic glasses after gamma irradiation at 4.2 °K by electron spin resonance spectroscopy

Abstract

Several organic glasses which are known to form trapped electrons when gamma irradiated at 77 °K have been irradiated at 4.2 °K and examined by electron spin resonance (e.s.r.) at the same temperature. In each case an absorption is observed which is probably due to trapped electrons. In three cases, the yield of trapped electrons at 4.2 °K seems to be as great as at 77 °K. In one case, a glassy alkane, the yield is enhanced at 4.2 °K. Trapped electrons in ethanol give a narrower e.s.r. line at 4.2 °K than at 77 °K, suggesting less orientation in the solvent cage.Trapped hydrogen atoms are not detected after irradiation at 4.2 °K. Contrary to prediction, hydrogen atoms are also not detected after post-irradiation photolysis of the trapped electrons.The results suggest that electron traps exist prior to irradiation and that molecular orientation via electronic dipole interaction is not a necessary condition for electron trapping. The results do not distinguish between trapping in solvent defects or trapping via electron-induced polarization of molecular orbitals.

Electron spin resonance study of trapped electrons in irradiated organic glasses at 4.2 °K

“…According to the results so far mentioned, it is concluded that, not only in non-polar glass but also in polar glass, the electrons liberated from the matrix molecules by ionizing radiations may be trapped with or without molecular orientation. Smith and Pieroni reached a similar conclusion (4). The results also lead to the conclusion that the width of the e.s.r.…”

“…Conclusion (b), already suggested in ref. 4, is further supported by conclusion (a). The change of the surroundings has probably resulted from the orientation of the ethanol molecules induced by the electrons themselves, so that the H atoms of the hydroxyl groups come closer to the electrons, giving the stronger hyperfine interaction and the wider e.s.r.…”

Optical and Thermal Bleaching of Trapped Electrons in Aliphatic Amine Glasses

“…spectra of the trapped electrons at an annealing temperature higher than -196 "C may be attributed to relaxation of electron trapping sites which is presumably due to re-orientation of the solvent dipoles around the trapped electrons. Similar phenomena were previously observed for trapped electrons in glassy ethanol and methyltetrahydrofuran upon warming from 4 to 77 "K after y-irradiation at 4 O K (10,11). Optical studies of trapped electrons in alcohol glasses also revealed the effect of such matrix relaxation on the optical absorption spectra of the trapped electrons (12)(13)(14).…”

Shallow and deep trap states of solvated electrons in methanol and their formation, electronic excitation, and relaxation dynamics

“…This is consistent with the previously discussed concept of the excess electron as "a trap-seeker and not a trap digger". [12][13][14] The dynamics dramatically changes after 2 OH-, 3 OH-and 4 OH-cavities are formed: the solvated electron now behaves as a "trap-digger". While the electron resides in the same cavity, the methanol molecules initially coordinating their CH 3 -group to the excess electron gradually reorient themselves to coordinate their OH-group.…”

“…12 The shallow trap state with a near-infrared absorption band was identified in low-temperature (4-77 K) glass, and its transformation to a deep trap state was observed at temperatures above 77 K, based on the emergence of a visible absorption band. 13,14 A recent femtosecond pump-probe photoemission spectroscopy study of e − met found that the vertical electron binding energy (VBE) for these two trap states is 2.1 eV (shallow) and 3.4 eV (deep), and that the transformation from the shallow to the deep trap state takes place within tens of picoseconds under ambient conditions. 12 Such multiple trap states have not been identified for e − sol in water or ammonia.…”