Electron trapping and hydrogen atoms in oxide glasses

Journal Article · Wed Sep 01 04:00:00 EDT 1999 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.479740· OSTI ID:6432673

Shkrob, I A; Tadjikov, B M; Chemerisov, S D; Trifunac, A D ^[1]

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1. Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

Trapped hydrogen atoms generated in 3 MeV [beta]-radiolysis of B[sub 2]O[sub 3]:OH glass below 140 K were studied using electron paramagnetic resonance (EPR). Two types of trapped H atoms were present in this glass; one was an interstitial atom located in a void between several BOB fragments, another was the atom trapped in a cage between two B[sub 3]O[sub 6] (boroxol) rings connected by hydrogen bonds. The geometry of the trapping site was determined using electron spin echo envelope modulation (ESEEM) spectroscopy. Time-resolved pulsed EPR was used to observe mobile H atoms at 300[endash]500 K. The lifetimes (10[endash]100 [mu]s) of the H atoms were controlled by [approximately]10[sup 18] hthinsp;cm[sup [minus]3] of metastable spin centers. The H atoms migrated with diffusion constant of 1.5[times]10[sup 7] hthinsp;cm[sup 2]/s (activation energy of 0.13[endash]0.16 eV), mean residence time at the site of 4[endash]5 ns, and mean jump length of 0.56 nm (at 300 K). This site-to-site migration causes rapid spin relaxation due to modulation of magnetic interactions, such as dipole[endash]dipole interaction of the unpaired electron of the H atom with [sup 10]B and [sup 11]B nuclei. Though there was no observed H/D kinetic isotope effect on the decay/diffusion of the hydrogen atoms, there was a significant isotope effect on their radiolytic yield ([alpha][approx]1.5[endash]1.6). This effect is comparable to the one observed in SiO[sub 2]:OH and aqueous acid glasses. This similarity suggests that in the room-temperature [open quotes]wet[close quotes] SiO[sub 2] and B[sub 2]O[sub 3] glasses, mobile H atoms are generated via electron trapping at the proton(s) associated with threefold coordinated oxygen ([endash]OH[sub 2][sup +] and/or [gt]OH[sup +] centers). Semiempirical MNDO simulations were used to estimate energetics of such electron trapping reactions.

• OSTI ID: 6432673
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Vol. 111:11; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
BORON COMPOUNDS
BOROSILICATE GLASS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DECOMPOSITION
ELECTRON SPIN RESONANCE
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
GLASS
HYDROGEN
HYDROXYL RADICALS
IMPURITIES
INTERSTITIALS
LEPTONS
MAGNETIC RESONANCE
NONMETALS
OXYGEN COMPOUNDS
POINT DEFECTS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADICALS
RADIOLYSIS
RESONANCE
TRAPPED ELECTRONS
TRAPPING