Evidence for a second kind of trapped electron in some deuterated aqueous glasses at low temperatures. A pulse radiolysis study

Abstract

. Can. J. Chem. 54, 367 (1976).Several deuterated aqueous glasses have been pulse-irradiated at 76 K. In addition to the well known visible absorption band of e,-, a second intense infrared absorption band, with A,,, > 3200 nm, has been found in ( a ) 50% by volume ethylene glycol, ( b ) 9.5 M LiC1, and ( c ) 2.5 and 4 M MgClz glasses. Electron scavengers decrease the intensities of both bands, but to different extents. An increase in temperature decreases the intensity of the infrared band, but not that of the visible band. These and other features lead us to conclude that the infrared band is due to shallowly trapped electrons which are distinctly different from trapped electrons which absorb in the visible region.The decay of the infrared band extends over several orders of magnitude in time and, unlike that of the visible band, is independent of wavelength. In the two chloride glasses the decay of the infrared band is accompanied by emission (A,,, = 410 nm) and is probably due to a spur reaction between an electron and hydroxyl radical t o form excited hydroxide ion. No emission is found in the ethylene glycol glass, but growth of the visible band matches the decay of the infrared band in this case.By comparing the amount of Ago produced in an ethylene glycol glass containing Ag+ with the decrease in intensity of the infrared and visible bands, we obtain '1400 = (5.7 + 0.8) X lo3 M-1 cm-I. From the shape of the infrared band, which is Lorentzian on the high energy side, we estimate A, , ,

A study of trapped electrons in LiCl/D2O and other aqueous glasses at temperatures down to 2 K by radiolysis, pulse radiolysis, photolysis, and stimulated luminescence

“…Above 1300 nm this absorption has a shape identical to that of e,,-as presented in ref. 2. This is further, strong evidence that the ir band is due to a trapped electron since no other species seems to be common to the uv photolysis of 9.5 M LiCl/D20/5 x M tryp glass and the radiolysis of the LiCl/D20, MgC12/D20, and ethylene glycol/D20 glasses.…”

“…Pulse radiolysis experiments were carried out as described earlier (2,3) with the exception that the samples were irradiated in a Janis model 8DT Super Varitemp cryostat in which the samples were cooled with a flow of cold helium gas (10). The temperature was maintained within f 0.5 K of the desired value by a Lake Shore Cryotronics model DRC-70C temperature controller and the temperature of the sample was measured with a silicon diode sensor situated very close to the sample.…”

“…Recently it was found by pulse radiolysis that substantial yields of two distinct types of trapped electrons, evis-and ei,-, are formed at low temperatures in some aqueous glasses and in both pure and doped ice crystals (1)(2)(3). The species evis-is the oft-studied species with an optical absorption band centered around 600 nm.…”

A pulse radiolysis study of trapped electrons in aqueous ethylene glycol glasses

“…The band due to e,, has A, , , = 650 nm but the apparent maximum shifts to higher wavelengths for spectra dominated by the infrared band due to e,. The maximum for e, has been estimated to be 3600 nm in MgC12/D20 (1).…”

“…In publications from this laboratory, pulse radiolysis experiments have been interpreted as indicating that e, and e,, are electrons trapped in two distinctly different molecular environments both in certain aqueous glasses (1 -4, 8, 9) and in crystalline ice (10, 1 l), although the conversion of e.; into e,, is readily observable in some aqueous glasses (1,8,12) including aqueous EG glasses (I). Dolivo and Kevan (13), on the other hand, have argued that the essential difference between the two types of electron is that e. : has a first solvation shell of water molecules which are not at equilibrium, whereas the water molecules immediately adjacent to e,, are at equilibrium.…”