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Radiation yield of oxygen-based radicals in hyperquenched glassy water gamma-irradiated at 77 K
PERGAMON
Radiation Physics and Chemistry Radiation Physics and Chemistry 53 (1998) 635±638
Short communication
Radiation yield of oxygen-based radicals in hyperquenched glassy water gamma-irradiated at 77 K Janusz Bednarek a, Andrzej Plonka a, Andreas Hallbrucker b, Erwin Mayer b a
Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Institut fuÈr Allgemeine, Anorganische und Theoretische Chemie, UniversitaÈt Innsbruck, Innrain 52A, A-6020 Innsbruck, Austria
b
Received 11 July 1997; accepted 28 July 1997
Abstract Hyperquenching of liquid water with cooling rates of 106±107 K sÿ1 yields glassy water. Upon g-irradiation at 77 K, the only paramagnetic species accumulating in hyperquenched glassy water are the hydroxyl and hydroperoxyl radicals. There are no hydrogen atoms or electrons seen by the ESR technique. For irradiation doses up to about 70 kGy, the relative contributions of hydroxyl and hydroperoxyl radicals to the total amount of paramagnetic species remain virtually constant. The total amount of paramagnetic species, n, is sublinear in dose, d, well approximated by n = 8.55 1016d 0.8 for n in spin gÿ1 and d in kGy. # 1998 Elsevier Science Ltd. All rights reserved.
1. Introduction Glassy water, known (BruÈggeler and Mayer, 1980) since 1980, can now routinely be made in gram-quantities by so-called ``hyperquenching'' of micrometersized water droplets on a solid cryoplate (Mayer, 1988). A variant of the original method is also available (Kim et al., 1993). In the original method, the estimated (Bachmann and Mayer, 1987) and calculated (Bald, 1986) cooling rates are of the order of 106± 107 K sÿ1. The structure of the hyperquenched glassy water (HGW) has been studied by dierential scanning calorimetry (Hallbrucker and Mayer, 1987; Hallbrucker et al., 1989; Johari et al., 1987, 1990), Xray, neutron (Bellisent-Funel et al., 1992; Hallbrucker et al., 1991) and electron (Dubochet et al., 1983) diffraction, infrared spectroscopy (Kim et al., 1993; Mayer, 1985), dielectric relaxation (Johari et al., 1992), and hole burning (Kim et al., 1995; Reinot et al., 1996). For HGW, on heating at 30 K minÿ1, the onset of glass±liquid transition (Hallbrucker et al., 1989; Johari et al., 1987, 1990), Tg, is at 136 K.
The structure of HGW diers from that of liquid water at ambient temperature in that liquid water on supercooling undergoes structural changes giving a more open, fully hydrogen bonded tetrahedral network (Bellisent-Funel et al., 1992; Hallbrucker et al., 1991). Even so, the glassy water is to be recognized as the best model for liquid water in radiation cryochemistry, especially for dilute aqueous solutions in their glassy states which can be obtained by hyperquenching of the liquids. In slow-cooled aqueous solutions where ice is formed and phase separation of the solute occurs, the paramagnetic species like OH radicals trapped in the ice compartments are unable to react with solutes because these are segregated into the ``freeze-concentration'' regions (Gregoli et al., 1982; Plonka, 1990; Riederer et al., 1983). The use of high concentration of additives, like electrolytes, to slow down the crystallization of ice and to obtain a glass even on slow cooling bears the disadvantage (Plonka, 1990) of formation of radicals from the additives that obscure the reactions of radicals originating from water radiolysis. Recognizing the unique opportunities to overcome
0969-806X/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 7 ) 0 0 2 7 2 - 7
636
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
these problems, we have started the ESR studies on radiation chemistry of HGW (Bednarek et al., 1996). 2. Experimental HGW was prepared by hyperquenching of aerosol droplets on a copper substrate held at 77 K. Water droplets of about 5 mm diameter size made by means of an ultrasonic nebulizer (HICO Ultrasonat, model 706E, operating at 1.7 MHz, droplet size according to company speci®cations) were suspended in gaseous nitrogen (99.999%) and passed into a high-vacuum cryostat through a 300 mm aperture. Once inside, the droplets moved at supersonic speed toward the substrate and deposited on it. 1 h deposition produced a 2±3 mm thick opaque layer of glassy solid water with a porcelain-like appearance and texture. According to X-ray diractograms it contained at most 5% crystalline, mainly cubic ice. DSC studies of HGW deposited on a copper plate, on a brass plate, or on IR transmitting materials gave identical results. All transfers of the sample from one container to the other were made when immersed in liquid N2. The g-irradiations were performed at 77 K at a dose rate of about 3 kGy hÿ1, controlled by a home-made electronic dosimeter calibrated against the standard Fricke dosimeter. The ESR spectra were recorded with an X-band ER 200DSRC spectrometer, on line with ESP 3220-200SH data acquisition and processing system (Bruker, Analyt. Messtechnik GmbH). As the standard for quantitative measurements the dilute (approx. 1.5 mM) benzene solution of DPPH was used. Its concentration was determined by optical spectroscopy at 520 nm; the extinction coecient is 12,000 Mÿ1 cmÿ1. The ESR signal intensity for irradiated HGW samples was corrected for the decrease of intensity (of about 50%) caused by the use of copper strip as sample support. 3. Results and discussion As for normal hexagonal ice, Ih, formed from liquid water by slow cooling in liquid nitrogen, we were unable to detect in HGW g-irradiated at 77 K either trapped hydrogen atoms or trapped electrons. This means that the hyperquenched glassy water does not provide good trapping sites for hydrogen atoms and this is in contrast to a number of aqueous binary systems that freeze to give glasses (Riederer et al., 1983). The same is true for trapped electrons. They were highly expected (Kroh and Plonka, 1977) but there was complete absence of any colour or ESR signal attributable to trapped electrons. The entire ESR spectrum of HGW g-irradiated at 77 K, cf. inset to Fig. 1, is due to oxygen-based rad-
Fig. 1. Accumulation of oxygen-based radicals in hyperquenched glassy water (HGW) upon g-irradiation at 77 K. The inset shows their ESR spectra (irradiation doses 0.5 and 66 kGy) which, according to the analysis (Bednarek et al., 1996), consists of approximately equal contributions of OH and HO2 radicals. The solid line is calculated according to relation (1), the dashed line corresponds to the radiation yield of 0.83 spins/100 eV.
icals. This spectrum, according to our recent analysis (Bednarek et al., 1996), consists of two components of about equal contributions for the whole range of irradiation doses. One of them, decaying completely at about 100 K, is typical for OH radicals trapped in glassy matrices. The second one, gaining resolution for samples annealed at about 140 K, is due to HO2 radicals. Evidently the HO2 radicals in glassy water are formed in much earlier stages of g-radiolysis than those in g-radiolysis of crystalline or polycrystalline Ih ices where they are formed in tiny amounts in secondary reactions of OH radicals. In ice Ih the OH radicals seem to be trapped in the original sites of water ionization, cf. left-hand side of Scheme 1 showing the ionization event of H2O molecule in a local con®guration of C2v pentamer symmetry. In HGW there was envisaged an additional reaction, cf. right-hand side of Scheme 1, occurring at Bjerrumlike L-defects present in relatively high concentrations in this system. According to Devlin (1990), isotopic exchange data of isolated D2O in H2O ice clearly reveal that amorphous ice is rich in Bjerrum-like L-
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
637
Scheme 1.
defects or shallow proton traps, in comparison to ice I. The required oxygen±oxygen bond for formation of HO2 radical may arise incipiently as a weak three-electron bond. Because it may be necessary to invoke the participation of excited species for this reaction we have postulated (Bednarek et al., 1996) a concerted process of the type depicted in Scheme 1 with O±O bond formation, loss of H2, and formation of H3O+ occurring at about the same time. Here it seems proper to add that already two decades ago it was suggested (Brocklehurst, 1977) that in water there could be formed a dimer cation, H2 O 2 , reactive no doubt, but strongly stabilized with respect to dissociation. It was stressed that when liquid water is ionized, hydrogenbonded molecules react extremely rapidly by proton
transfer. However, there was a view that water contains some interstitial molecules which are not hydrogen-bonded at all and such molecules might well attack the cage of bonded molecules around them to form dimer cations. Hydrogen bonding was expected to increase the energy needed to ionize the lone pairs, so that charge may be localized preferentially on the interstitial molecules. The accumulation of oxygen-based radicals in HGW upon g-irradiation at 77 K is shown in Fig. 1. It might be thought to be linear up to, at most, 10 kGy with the radiation yield of about 0.83 spins/100 eV, cf. the dashed line in Fig. 1. So we are rather far from the value 4.8 estimated for OH radicals in liquid water at room temperature (Buxton et al., 1988), rather close to
638
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
ice Ih with radiation yield of OH radicals equal to 0.6± 0.9. We have to note (Kevan, 1968), however, that in ice Ih the yield±dose curve for OH radicals is linear only to about 1 kGy. For the whole irradiation dose range, cf. solid line in Fig. 1, our experimental data are well approximated by n 8:55 1016 d 0:8
1
for the concentration n in spin gÿ1 and the dose d in kGy. Thus there is no doubt that recent conclusions (Klassen, 1996) about ice Ih remain valid to some extent for HGW. In ice, as compared to liquid water, a higher proportion of electrons react with H3O+, see Scheme 1; the combination of two H atoms to form H2 is favoured, the combination of two OH radicals to form H2O2 is slower, and ®nally the back reactions of radicals with H2O2 are slower. Contrary to ice Ih, in HGW the radiation produced oxygen-based radicals are reactive towards the solute (Bednarek et al., 1998).
Acknowledgements This work was supported in part by KBN Grant No. 3 T09A 02510 (J. B. and A. P.) and by Forschungsforderungsfond of Austria, Project P 12319-PHY (A. H. and E. M.). The authors are also grateful to Dr. B. Brocklehurst for his comments on formation of the dimer H2 O 2. References Bachmann, L. and Mayer, E., 1987. Physics of water and ice: Implications for cryo®xation. In: Steinbrecht, R.A., Zierold, K. (Eds.), Cryotechniques in Biological Electron Microscopy. Springer-Verlag, Berlin p. 3. Bald, W.B., 1986. On crystal size and cooling rate. J. Microsc. 143, 89. Bednarek, J., Plonka, A., Hallbrucker, A., Mayer, E., Symons, M.C.R., 1996. Hydroperoxyl radical generation by g-irradiation of glassy water at 77 K. J. Am. Chem. Soc. 118, 9387. Bednarek, J., Plonka, A., Hallbrucker, A. and Mayer, E., 1998. In preparation. Bellisent-Funel, M.C., Bosio, L., Hallbrucker, A., Mayer, E., Sridi-Dorbez, R., 1992. X-ray and neutron scattering studies of the structure of hyperquenched glassy water. Chem. Phys. 97, 1282. Brocklehurst, B., 1977. A general discussion on radiation eects in liquids and solids, 23±25 March 1977, University of Leicester. Faraday Discuss. Chem. Soc. 63, 280. BruÈggeler, P., Mayer, E., 1980. Complete vitri®cation in pure liquid water and dilute aqueous solutions. Nature 288, 569. Buxton, G.V., Greenstock, C.L., Helman, W.P., Ross, A.B., 1988. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals
OH= Oÿ in aqueous solution. J. Phys. Chem. Ref. Data 17, 513. Devlin, J.P., 1990. Vibrational spectra and point defect activities of icy solids and gas phase clusters. Int. Rev. Phys. Chem. 9, 29. Dubochet, J., Adrian, M., Vogel, R.H., 1983. Amorphous solid water obtained by vapor condensation or by liquid cooling: A comparison in the electron microscope. CryoLett. 4, 233. Gregoli, S., Olast, M., Bertingchamps, A., 1982. Radiolytic pathways in g-irradiated DNA: In¯uence of chemical and conformational factors. Radiat. Res. 89, 238. Hallbrucker, A., Mayer, E., 1987. Calorimetric study of the vitri®ed liquid water to cubic ice phase transition. J. Chem. Phys. 91, 503. Hallbrucker, A., Mayer, E., Johari, G.P., 1989. The heat capacity and glass transition of hyperquenched glassy water. Philos. Mag. B60, 179. Hallbrucker, A., Mayer, E., O'Mard, L.P., Dore, J.C., Chieux, P., 1991. Structural characterization of hyperquenched glassy water and vapor-deposited amorphous ice. Phys. Lett. A159, 406. Johari, G.P., Hallbrucker, A., Mayer, E., 1987. The glass± liquid transition of hyperquenched water. Nature 330, 552. Johari, G.P., Hallbrucker, A., Mayer, E., 1990. Isotope eect on the glass transition and crystallization of hyperquenched glassy water. J. Chem. Phys. 92, 6742. Johari, G.P., Hallbrucker, A., Mayer, E., 1992. Dielectric study of the structure of hyperquenched glassy water and its crystallized form. J. Chem. Phys. 97, 5851. Kevan, L., 1968. Radiation chemistry of frozen aqueous solutions. In: Stein, G. (Ed.), Radiation Chemistry of Aqueous Systems. The Weizmann Science Press of Israel, Jerusalem p. 21. Kim, W.-H., McPhillen, M., Hayes, J.M., Small, G.J., 1993. A new methodology for production of hyperquenched glassy ®lms and their study by nonphotochemical hole burning. Chem. Phys. Lett. 207, 443. Kim, W.-H., Reinot, T., Hayes, J.M., Small, G.J., 1995. Hyperquenched glassy ®lms of water: A study by hole burning. J. Phys. Chem. 99, 7300. Klassen, N.V., 1996. Ice near 08C: Radiolysis and absorbed dose calorimetry. Radiat. Phys. Chem. 48, 281. Kroh, J., Plonka, A., 1977. Electron trapping in frozen gels girradiated at 77 K. Chem. Phys. Lett. 52, 371. Mayer, E., 1985. Infrared spectrum of vitri®ed liquid water. A comparison with the vapor deposited amorphous form. J. Phys. Chem. 89, 3474. Mayer, E., 1988. Hyperquenching of water and dilute aqueous solutions into their glassy states: an approach to cryo®xation. Cryo-Lett. 9, 66. Plonka, A., 1990. ESR studies on reactivity of radiation produced species in condensed media. Magn. Res. Rev. 15, 83. Reinot, T., Kim, W.-H., Hayes, J.M., Small, G.J., 1996. Electronic dephasing of APT in glassy ®lms of water from 5 to 100 K: Implications for H-bonding liquids. J. Chem. Phys. 104, 793. Riederer, H., Hutterman, J., Boon, P., Symons, M.C.R., 1983. Hydroxyl radicals in aqueous glasses: Characterization and reactivity studied by ESR spectroscopy. J. Magn. Res. 54, 54.
Radiation Physics and Chemistry Radiation Physics and Chemistry 53 (1998) 635±638
Short communication
Radiation yield of oxygen-based radicals in hyperquenched glassy water gamma-irradiated at 77 K Janusz Bednarek a, Andrzej Plonka a, Andreas Hallbrucker b, Erwin Mayer b a
Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Institut fuÈr Allgemeine, Anorganische und Theoretische Chemie, UniversitaÈt Innsbruck, Innrain 52A, A-6020 Innsbruck, Austria
b
Received 11 July 1997; accepted 28 July 1997
Abstract Hyperquenching of liquid water with cooling rates of 106±107 K sÿ1 yields glassy water. Upon g-irradiation at 77 K, the only paramagnetic species accumulating in hyperquenched glassy water are the hydroxyl and hydroperoxyl radicals. There are no hydrogen atoms or electrons seen by the ESR technique. For irradiation doses up to about 70 kGy, the relative contributions of hydroxyl and hydroperoxyl radicals to the total amount of paramagnetic species remain virtually constant. The total amount of paramagnetic species, n, is sublinear in dose, d, well approximated by n = 8.55 1016d 0.8 for n in spin gÿ1 and d in kGy. # 1998 Elsevier Science Ltd. All rights reserved.
1. Introduction Glassy water, known (BruÈggeler and Mayer, 1980) since 1980, can now routinely be made in gram-quantities by so-called ``hyperquenching'' of micrometersized water droplets on a solid cryoplate (Mayer, 1988). A variant of the original method is also available (Kim et al., 1993). In the original method, the estimated (Bachmann and Mayer, 1987) and calculated (Bald, 1986) cooling rates are of the order of 106± 107 K sÿ1. The structure of the hyperquenched glassy water (HGW) has been studied by dierential scanning calorimetry (Hallbrucker and Mayer, 1987; Hallbrucker et al., 1989; Johari et al., 1987, 1990), Xray, neutron (Bellisent-Funel et al., 1992; Hallbrucker et al., 1991) and electron (Dubochet et al., 1983) diffraction, infrared spectroscopy (Kim et al., 1993; Mayer, 1985), dielectric relaxation (Johari et al., 1992), and hole burning (Kim et al., 1995; Reinot et al., 1996). For HGW, on heating at 30 K minÿ1, the onset of glass±liquid transition (Hallbrucker et al., 1989; Johari et al., 1987, 1990), Tg, is at 136 K.
The structure of HGW diers from that of liquid water at ambient temperature in that liquid water on supercooling undergoes structural changes giving a more open, fully hydrogen bonded tetrahedral network (Bellisent-Funel et al., 1992; Hallbrucker et al., 1991). Even so, the glassy water is to be recognized as the best model for liquid water in radiation cryochemistry, especially for dilute aqueous solutions in their glassy states which can be obtained by hyperquenching of the liquids. In slow-cooled aqueous solutions where ice is formed and phase separation of the solute occurs, the paramagnetic species like OH radicals trapped in the ice compartments are unable to react with solutes because these are segregated into the ``freeze-concentration'' regions (Gregoli et al., 1982; Plonka, 1990; Riederer et al., 1983). The use of high concentration of additives, like electrolytes, to slow down the crystallization of ice and to obtain a glass even on slow cooling bears the disadvantage (Plonka, 1990) of formation of radicals from the additives that obscure the reactions of radicals originating from water radiolysis. Recognizing the unique opportunities to overcome
0969-806X/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 7 ) 0 0 2 7 2 - 7
636
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
these problems, we have started the ESR studies on radiation chemistry of HGW (Bednarek et al., 1996). 2. Experimental HGW was prepared by hyperquenching of aerosol droplets on a copper substrate held at 77 K. Water droplets of about 5 mm diameter size made by means of an ultrasonic nebulizer (HICO Ultrasonat, model 706E, operating at 1.7 MHz, droplet size according to company speci®cations) were suspended in gaseous nitrogen (99.999%) and passed into a high-vacuum cryostat through a 300 mm aperture. Once inside, the droplets moved at supersonic speed toward the substrate and deposited on it. 1 h deposition produced a 2±3 mm thick opaque layer of glassy solid water with a porcelain-like appearance and texture. According to X-ray diractograms it contained at most 5% crystalline, mainly cubic ice. DSC studies of HGW deposited on a copper plate, on a brass plate, or on IR transmitting materials gave identical results. All transfers of the sample from one container to the other were made when immersed in liquid N2. The g-irradiations were performed at 77 K at a dose rate of about 3 kGy hÿ1, controlled by a home-made electronic dosimeter calibrated against the standard Fricke dosimeter. The ESR spectra were recorded with an X-band ER 200DSRC spectrometer, on line with ESP 3220-200SH data acquisition and processing system (Bruker, Analyt. Messtechnik GmbH). As the standard for quantitative measurements the dilute (approx. 1.5 mM) benzene solution of DPPH was used. Its concentration was determined by optical spectroscopy at 520 nm; the extinction coecient is 12,000 Mÿ1 cmÿ1. The ESR signal intensity for irradiated HGW samples was corrected for the decrease of intensity (of about 50%) caused by the use of copper strip as sample support. 3. Results and discussion As for normal hexagonal ice, Ih, formed from liquid water by slow cooling in liquid nitrogen, we were unable to detect in HGW g-irradiated at 77 K either trapped hydrogen atoms or trapped electrons. This means that the hyperquenched glassy water does not provide good trapping sites for hydrogen atoms and this is in contrast to a number of aqueous binary systems that freeze to give glasses (Riederer et al., 1983). The same is true for trapped electrons. They were highly expected (Kroh and Plonka, 1977) but there was complete absence of any colour or ESR signal attributable to trapped electrons. The entire ESR spectrum of HGW g-irradiated at 77 K, cf. inset to Fig. 1, is due to oxygen-based rad-
Fig. 1. Accumulation of oxygen-based radicals in hyperquenched glassy water (HGW) upon g-irradiation at 77 K. The inset shows their ESR spectra (irradiation doses 0.5 and 66 kGy) which, according to the analysis (Bednarek et al., 1996), consists of approximately equal contributions of OH and HO2 radicals. The solid line is calculated according to relation (1), the dashed line corresponds to the radiation yield of 0.83 spins/100 eV.
icals. This spectrum, according to our recent analysis (Bednarek et al., 1996), consists of two components of about equal contributions for the whole range of irradiation doses. One of them, decaying completely at about 100 K, is typical for OH radicals trapped in glassy matrices. The second one, gaining resolution for samples annealed at about 140 K, is due to HO2 radicals. Evidently the HO2 radicals in glassy water are formed in much earlier stages of g-radiolysis than those in g-radiolysis of crystalline or polycrystalline Ih ices where they are formed in tiny amounts in secondary reactions of OH radicals. In ice Ih the OH radicals seem to be trapped in the original sites of water ionization, cf. left-hand side of Scheme 1 showing the ionization event of H2O molecule in a local con®guration of C2v pentamer symmetry. In HGW there was envisaged an additional reaction, cf. right-hand side of Scheme 1, occurring at Bjerrumlike L-defects present in relatively high concentrations in this system. According to Devlin (1990), isotopic exchange data of isolated D2O in H2O ice clearly reveal that amorphous ice is rich in Bjerrum-like L-
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
637
Scheme 1.
defects or shallow proton traps, in comparison to ice I. The required oxygen±oxygen bond for formation of HO2 radical may arise incipiently as a weak three-electron bond. Because it may be necessary to invoke the participation of excited species for this reaction we have postulated (Bednarek et al., 1996) a concerted process of the type depicted in Scheme 1 with O±O bond formation, loss of H2, and formation of H3O+ occurring at about the same time. Here it seems proper to add that already two decades ago it was suggested (Brocklehurst, 1977) that in water there could be formed a dimer cation, H2 O 2 , reactive no doubt, but strongly stabilized with respect to dissociation. It was stressed that when liquid water is ionized, hydrogenbonded molecules react extremely rapidly by proton
transfer. However, there was a view that water contains some interstitial molecules which are not hydrogen-bonded at all and such molecules might well attack the cage of bonded molecules around them to form dimer cations. Hydrogen bonding was expected to increase the energy needed to ionize the lone pairs, so that charge may be localized preferentially on the interstitial molecules. The accumulation of oxygen-based radicals in HGW upon g-irradiation at 77 K is shown in Fig. 1. It might be thought to be linear up to, at most, 10 kGy with the radiation yield of about 0.83 spins/100 eV, cf. the dashed line in Fig. 1. So we are rather far from the value 4.8 estimated for OH radicals in liquid water at room temperature (Buxton et al., 1988), rather close to
638
J. Bednarek et al. / Radiation Physics and Chemistry 53 (1998) 635±638
ice Ih with radiation yield of OH radicals equal to 0.6± 0.9. We have to note (Kevan, 1968), however, that in ice Ih the yield±dose curve for OH radicals is linear only to about 1 kGy. For the whole irradiation dose range, cf. solid line in Fig. 1, our experimental data are well approximated by n 8:55 1016 d 0:8
1
for the concentration n in spin gÿ1 and the dose d in kGy. Thus there is no doubt that recent conclusions (Klassen, 1996) about ice Ih remain valid to some extent for HGW. In ice, as compared to liquid water, a higher proportion of electrons react with H3O+, see Scheme 1; the combination of two H atoms to form H2 is favoured, the combination of two OH radicals to form H2O2 is slower, and ®nally the back reactions of radicals with H2O2 are slower. Contrary to ice Ih, in HGW the radiation produced oxygen-based radicals are reactive towards the solute (Bednarek et al., 1998).
Acknowledgements This work was supported in part by KBN Grant No. 3 T09A 02510 (J. B. and A. P.) and by Forschungsforderungsfond of Austria, Project P 12319-PHY (A. H. and E. M.). The authors are also grateful to Dr. B. Brocklehurst for his comments on formation of the dimer H2 O 2. References Bachmann, L. and Mayer, E., 1987. Physics of water and ice: Implications for cryo®xation. In: Steinbrecht, R.A., Zierold, K. (Eds.), Cryotechniques in Biological Electron Microscopy. Springer-Verlag, Berlin p. 3. Bald, W.B., 1986. On crystal size and cooling rate. J. Microsc. 143, 89. Bednarek, J., Plonka, A., Hallbrucker, A., Mayer, E., Symons, M.C.R., 1996. Hydroperoxyl radical generation by g-irradiation of glassy water at 77 K. J. Am. Chem. Soc. 118, 9387. Bednarek, J., Plonka, A., Hallbrucker, A. and Mayer, E., 1998. In preparation. Bellisent-Funel, M.C., Bosio, L., Hallbrucker, A., Mayer, E., Sridi-Dorbez, R., 1992. X-ray and neutron scattering studies of the structure of hyperquenched glassy water. Chem. Phys. 97, 1282. Brocklehurst, B., 1977. A general discussion on radiation eects in liquids and solids, 23±25 March 1977, University of Leicester. Faraday Discuss. Chem. Soc. 63, 280. BruÈggeler, P., Mayer, E., 1980. Complete vitri®cation in pure liquid water and dilute aqueous solutions. Nature 288, 569. Buxton, G.V., Greenstock, C.L., Helman, W.P., Ross, A.B., 1988. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals
OH= Oÿ in aqueous solution. J. Phys. Chem. Ref. Data 17, 513. Devlin, J.P., 1990. Vibrational spectra and point defect activities of icy solids and gas phase clusters. Int. Rev. Phys. Chem. 9, 29. Dubochet, J., Adrian, M., Vogel, R.H., 1983. Amorphous solid water obtained by vapor condensation or by liquid cooling: A comparison in the electron microscope. CryoLett. 4, 233. Gregoli, S., Olast, M., Bertingchamps, A., 1982. Radiolytic pathways in g-irradiated DNA: In¯uence of chemical and conformational factors. Radiat. Res. 89, 238. Hallbrucker, A., Mayer, E., 1987. Calorimetric study of the vitri®ed liquid water to cubic ice phase transition. J. Chem. Phys. 91, 503. Hallbrucker, A., Mayer, E., Johari, G.P., 1989. The heat capacity and glass transition of hyperquenched glassy water. Philos. Mag. B60, 179. Hallbrucker, A., Mayer, E., O'Mard, L.P., Dore, J.C., Chieux, P., 1991. Structural characterization of hyperquenched glassy water and vapor-deposited amorphous ice. Phys. Lett. A159, 406. Johari, G.P., Hallbrucker, A., Mayer, E., 1987. The glass± liquid transition of hyperquenched water. Nature 330, 552. Johari, G.P., Hallbrucker, A., Mayer, E., 1990. Isotope eect on the glass transition and crystallization of hyperquenched glassy water. J. Chem. Phys. 92, 6742. Johari, G.P., Hallbrucker, A., Mayer, E., 1992. Dielectric study of the structure of hyperquenched glassy water and its crystallized form. J. Chem. Phys. 97, 5851. Kevan, L., 1968. Radiation chemistry of frozen aqueous solutions. In: Stein, G. (Ed.), Radiation Chemistry of Aqueous Systems. The Weizmann Science Press of Israel, Jerusalem p. 21. Kim, W.-H., McPhillen, M., Hayes, J.M., Small, G.J., 1993. A new methodology for production of hyperquenched glassy ®lms and their study by nonphotochemical hole burning. Chem. Phys. Lett. 207, 443. Kim, W.-H., Reinot, T., Hayes, J.M., Small, G.J., 1995. Hyperquenched glassy ®lms of water: A study by hole burning. J. Phys. Chem. 99, 7300. Klassen, N.V., 1996. Ice near 08C: Radiolysis and absorbed dose calorimetry. Radiat. Phys. Chem. 48, 281. Kroh, J., Plonka, A., 1977. Electron trapping in frozen gels girradiated at 77 K. Chem. Phys. Lett. 52, 371. Mayer, E., 1985. Infrared spectrum of vitri®ed liquid water. A comparison with the vapor deposited amorphous form. J. Phys. Chem. 89, 3474. Mayer, E., 1988. Hyperquenching of water and dilute aqueous solutions into their glassy states: an approach to cryo®xation. Cryo-Lett. 9, 66. Plonka, A., 1990. ESR studies on reactivity of radiation produced species in condensed media. Magn. Res. Rev. 15, 83. Reinot, T., Kim, W.-H., Hayes, J.M., Small, G.J., 1996. Electronic dephasing of APT in glassy ®lms of water from 5 to 100 K: Implications for H-bonding liquids. J. Chem. Phys. 104, 793. Riederer, H., Hutterman, J., Boon, P., Symons, M.C.R., 1983. Hydroxyl radicals in aqueous glasses: Characterization and reactivity studied by ESR spectroscopy. J. Magn. Res. 54, 54.