A TEST OF THE INTRINSIC NATURE OF THE SHALLOW PROTON TRAPS IN ICE

P.J. WOOLDRIDGE; J.P. DEVLIN

doi:doi:10.1051/jphyscol:1987189

Numéro		J. Phys. Colloques Volume 48, Numéro C1, Mars 1987 VII^th Symposium on the Physics and Chemistry of Ice


Page(s)		C1-641 - C1-644
DOI		https://doi.org/10.1051/jphyscol:1987189

VII^th Symposium on the Physics and Chemistry of Ice

J. Phys. Colloques 48 (1987) C1-641-C1-644
DOI: 10.1051/jphyscol:1987189

A TEST OF THE INTRINSIC NATURE OF THE SHALLOW PROTON TRAPS IN ICE

P.J. WOOLDRIDGE et J.P. DEVLIN

Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, U.S.A.

Abstract
It was recently suggested by Warman and Kunst that the slow secondary decay of solvated electrons, generated in ice by pulsed-electron-beam radiolysis, is indicative of the presence of relatively shallow proton traps that delays the non-geminate recombination of proton-solvated electron pairs (1). Their model for the kinetics of the decay of e^- (sol), which extends into the microsecond range at 270 K invoked the presence of a pseudoequilibrium between mobile protons and protons immobilized by association with shallow traps. The traps were tentatively identified as Bjerrum L-defects which are known to have an associated partial negative charge (2). Additional strong evidence, for the importance of shallow proton traps in ice following radiolysis, was subsequently obtained from FT-IR spectroscopic study of proton exchange rates as a function of temperature (3). Although irradiation with 1.7 MeV electrons produced only limited proton exchange in cubic ice at 90 K, the subsequent warming of the samples into the 125 K range resulted in the rapid conversion of isolated D₂O to neighbor coupled HOD molecules. Since the thermal generation of the mobile protons required for this exchange reaction requires temperatures in excess of 135 K and results in the formation of isolated HOD (4), protons escaping from shallow traps were clearly responsible for the 125 K reaction. Since electron beam radiolysis generates numerous defects in ice and, when prolonged, can convert crystalline ice to amorphous ice, the rather conclusive evidence that protons are shallowly trapped in ice following radiolysis is only suggestive of the existence of such traps in pure ice. On the other hand, the question of the intrinsic or extrinsic nature of the traps is of considerable consequence in the analysis of both kinetic and thermodynamic properties of ion-pair defects in ice. For these reasons efforts to evaluate the nature of the shallow traps are warranted and one such effort, based on the photoionization of ice, is described.