Hydroperoxyl Radical Generation by γ-Irradiation of Glassy Water at 77 K

Abstract

ESR spectroscopy has been used to identify the paramagnetic species trapped at 77 K upon γ-irradiation of glassy water prepared by hyperquenching of liquid water at cooling rates exceeding 10 5 K/s. Besides OH radicals, which are the only paramagnetic intermediates of water radiolysis stabilized at 77 K in hexagonal ice prepared by slow cooling of liquid water, comparable amounts of HO 2 radicals were found in glassy water. The ESR spectra for trapped OH radicals were typical of such radicals in a glass. Neither trapped electrons nor trapped hydrogen atoms were detected. The contributions of OH and HO 2 radicals to the ESR spectra of glassy water do not depend on irradiation dose in the range 0.8-18 kGy. We stress that HO 2 radicals are not detected in irradiated hexagonal ice under these conditions. They are formed as secondary products after annealing to destroy the OH radicals, but the yields are tiny relative to the remarkably high yields observed in the glassy water. Possible mechanisms for HO 2 radical formation in the early stages of water radiolysis in the glassy state are discussed.

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

“…and in amorphous ice[107] are similar to each other, indicating that the detected HO Å is confined by hydrogen bonding with adjacent H 2 O molecules and SiOH groups. The hydrogen bonding quenches the angular momentum of the doubly-degenerate O 2pp orbitals accommodating the unpaired spin, and allows interstitial HO Å to be detectable by EPR.…”

Production of O2 on icy satellites by electronic excitation of low-temperature water ice

“…There is recent evidence that excited-state lifetimes in ice do increase with temperature 14,18 , in a manner suggestive of changes in the local hydrogen bonding. The dissociation fragments (O, OH) then reactively scatter to form a stable precursor molecule, possibly HO 2 or H 2 O 2 , which are known to be produced in irradiated ice 6,19,20 . A second electronic excitation then directly dissociates the precursor molecule to form O 2 .…”

Radicals Produced by γ-Irradiation of Hyperquenched Glassy Water Containing 2′-Deoxyguanosine-5′-monophosphate

“…There is no doubt that HO 2 · radicals are also present in these samples; their signal remains as the only spectral component after annealing at 120 K. This result refutes the above-mentioned supposition and supports the proposed mechanism of HO 2 · formation at L-type defect sites in the primary step of radiolysis. 7 It is relevant to add that HO 2 · radicals were also observed, after low-dose irradiation, in vapor-deposited amorphous solid water (prepared without ultrasonic treatment), which like HGW is rich in L-type defect sites. 8 As seen from Figure 1b, the significant fraction of crystalline ice in HGW made with a pneumatic nebulizer does not seem to have an effect on the HO 2 · yield.…”

“…The present results for irradiated HGW samples prepared with the use of ultrasonic nebulizer are consistent with the previous study. 7 ESR spectra consist of two components corresponding to OH · and HO 2 · radicals, which are formed in equal amounts. The total radical concentration determined in this work is 0.70 ( 0.04 mmol/ dm 3 at the absorbed dose of 8 kGy, in agreement with the radiation yield reported earlier, G ) 0.83 spins per 100 eV.…”