PROCEEDINGS OF THE INTERNATIONAL SCHOOL OF PHYSICS "ENRICO FERMI"_2 potx

This page intentionally left blank Hydrogen bonding at high pressure J S LOVEDAY Department of Physics and Astronomy and Centre for Science at Extreme Conditions The University of Edinburgh - Mayfield Rd, Edinburgh EH9 3JZ, Scotland, UK - Introduction The properties of the hydrogen bond are applicable to a wide range of fields They play a crucial role in many areas of biology: the base pairings in DNA are the result of H-bonds, the behaviour of water and other H-bonded solvents are crucial in chemistry, H-bonds and their directional nature are responsible for the structural versatility of ice giving rise to at least eleven phases below 2GPa, hydrogen bonding plays an important role in determining the dehydration properties of hydrous minerals, implicated as a possible cause of deep-focus earthquakes [1], and since the outer planets and their satellites contain large quantities of ice, ammonia and methane, the properties of these systems are crucial to planetary modelling This ubiquity provides a very powerful motivation to understand the microscopic behaviour of hydrogen bonding, including, the relationships between bonding strength, atomic species and bond geometry [2] — Definitions Figure shows a schematic of a hydrogen bond Atom A is covalently bonded to a hydrogen which hydrogen bonds to atom B Atom A is referred to as the donor and B the acceptor The criteria which determine if a particular contact is a hydrogen bond are somewhat subjective but consist of a combination of geometric and vibrational properties The principal criterion is that the H • • • B distance is less than the sum of the van der Waals radii of H and B —taking the value for H to be 1A [3] In addition, there is an expectation that the A-H stretch vibrational mode should soften and that © Societa Italiana di Fisica 357 358 J S LOVEDAY Atom A Donor Atom B Acceptor , Atom A Donor Atom B Acceptor H 6- Fig - A schematic diagram of long (upper) and short (lower) H-bonds the A-H • • • B libration mode should stiffen For long hydrogen bonds the interaction is considered to be largely ionic between a somewhat positive hydrogen atom —indicated by a 8+ in fig 1— and a somewhat negative atom B —indicated by a 6— As hydrogen bonds shorten, they develop a more covalent character with transfer of bonding electron density from A-H to H • • • B as shown The example shown is a simple linear H-bond, but it is possible to have poly-furcated hydrogen bonds where H forms bonds to more than one B atom, or B forms bonds to multiple H atoms Finally, B need not be an atom; it may be an accumulation of electron density as in ethyne where C-H forms H-bonds to the carbon-carbon triple bonds [4] — Techniques The principal microscopic properties needed to characterise a hydrogen bond are its geometry and the strength of the bonds; in addition, it is clearly important to understand the nature of the bonding As a result, for high pressure studies, the techniques generally used are optical and infra-red measurements of vibrational frequencies, diffraction studies to characterise the geometry, and ab initio modelling studies that explore the nature of the bonding Other techniques like nuclear magnetic resonance and neutron inelastic scattering have proved very powerful for studies of H-bonds at ambient pressure but have not yet been seriously applied at high pressure 3'1 Vibrational spectroscopy – Spectroscopy using photons was amongst the earliest techniques to be applied to H-bonding at high pressure Here the frequencies of modes of vibration are measured by their coupling to the incident light via a change in dipole moment (infra-red) or polarisability (Raman) The attraction of such measurements is that the softening of the A-H stretch mode (referred to here as the vibron) is one of the primary indications of strengthening hydrogen bonds, and this mode is easily identified for long hydrogen bonds Although spectroscopic data are relatively easy to measure, interpretation and mode assignment are often difficult In addition, one of the primary HYDROGEN BONDING AT HIGH PRESSURE 359 aims of spectroscopic studies has been to explore short H-bonds close to molecular dissociation Under these conditions the vibron moves into regions where diamonds have absorption bands and interaction between the vibron and other vibrational modes becomes significant However, innovations in cell design, improvements in the quality of IR data made possible by the use of synchrotron light sources, and the use of modelling in combination with experiments have led to considerable improvements in the quality of information available [5, 6] Other spectroscopic techniques have been used for measurements of vibrational frequencies including neutron [7] and X-ray [8] triple-axis studies of phonon dispersion, incoherent neutron spectroscopic measurements of density of states [9] and X-ray nuclear spectroscopy measurements of partial density of states [10] For H-bonded systems however, the vast bulk of spectroscopic data are obtained using photons For this reason the term spectroscopic used in this lecture refers to measurements of vibrational frequencies using Raman or IR methods 3'2 Structural studies - Diffraction studies are the only means to measure the geometry of H-bonds and are thus a crucial component of any attempt to characterise an H-bonded system Although X-ray studies are able to locate hydrogen atoms and can identify the H-bond contacts in a structure, neutron diffraction is the only technique able to measure the geometry sufficiently precisely Studies of H-bonded systems were a primary motivation of the development of high pressure neutron diffraction [11,12] and form a significant fraction of the studies performed The Paris-Edinburgh cell is now able to achieve a pressure of 30 GPa for such studies [11, 12] Although this represents a significant pressure range, it is not sufficient to explore dissociation of H-bonds in simple molecular systems Studies of dissociation of H-bonds in simple molecular solids remain an important motivation for further extensions of the pressure range 3'3 Ab initio modelling - The capabilities and accuracy of ab initio modelling studies have seen remarkable recent improvement Two basic methods exist to carry out such modelling In the first (static total-energy calculations) the total energy is computed for a fixed configuration of atoms and the best configuration is found by exploring the variation in total energy with change in configuration Static techniques have had success in studies of H-bonding [13, 14] but are limited by the difficulty of handling disorder The development of ab initio molecular dynamics (the Car-Parrinello method) [15] overcomes this limitation and has revolutionised modelling of H-bond systems In this method, the time evolution of the system is followed with the motion of the particles being determined from a self-consistent solution of the electronic Hamilitonian calculated at each time step Considerable effort has been put into development of techniques to handle the hydrogen atom as a quantum object [16] As a result, remarkable agreement between observation and modelling can be obtained Theoretical studies are generally not able to identify the structure ab initio, however, and require structural information as a start point 360 J S LOVEDAY 10 15 20 25 P(GPa) Fig - The measured pressure variation of the intramolecular O-D bond length in ice VIII [18] shown as open circles and the crosses are the results of Hartree-Fock calculations The dotted line shows the variation estimated from previous spectroscopic studies [17] — Molecular systems: water-ice The solid phases adopted by the water molecule have become model systems for studies of H-bonding at high pressure At the molecular level water is one of the simplest H-bonded systems since H-bonds are the principal attractive interaction As a result of this and because of the fundamental interest of the water molecule, ice has been extensively studied A further point of interest has been in the "centring" transition where the protons reach the centre of the hydrogen bond and ice becomes a simple oxide, "symmetric" ice X Early measurements of the hydrogen bond strength using spectroscopic methods showed a strong reduction in the O-H vibron indicating a weakening of the (covalent) molecular bond and a strengthening of the hydrogen bond [17] In the absence of direct measurements, estimates were made of the extension of the covalent O-H bond length resulting from this weakening This approach requires an assumption to be made about the changes in the potentials with pressure The assumption made was that the doublewell mean-field potential for the H-atom (shown in the right-hand plot of fig 3) could be described by the addition of two pressure-independent two-atom potentials (fig 3, lefthand plot) describing the interaction of the H-atom with the donor and acceptor oxygen atoms, respectively This assumption of pressure-independent two-atom potentials implies that as the H-bond compresses and the acceptor atom moves closer to the hydrogen the attraction of H by the acceptor causes the covalent O-H bond to lengthen, and this lengthening weakens the O-H bond to the donor oxygen This model had previously been found to describe well the relationships between O-H and vibron frequency and O • • • O determined from studies of a wide range of different H-bonded materials at ambient pressure [3] The first structural study carried out with the Paris-Edinburgh cell, studies of ice VIII, tested this assumption and showed that the intramolecular bond length was essentially unchanged by pressure up to at least 25GPa (fig 2) [18, 19] This lack of 361 HJ.YDROGEN BONDING AT HIGH PRESSURE Two-atom O-H potential Atom A Donor 8+ 5- -0.5 0.0 0.5 distance from h–bond centre(A) Fig - A schematic diagram showing how the full H-bond potential (right-hand plot) is built up from two-atom O-H potentials (left-hand plot) describing the interaction between the Elatom and the donor and acceptor oxygen atoms This approach and the assumption of a lack of change in the two-atom potentials with pressure underlies Klug and Whalley's [17] estimates of the variation of the O-H bond length with pressure shown in fig change in the bond length implies that the softening of the vibron can be interpreted as a changes of the curvature of the underlying two-atom O-H potentials —behaviour which is essentially the opposite of that which had been assumed Two total-energy studies reproduced the observed behaviour of the O-H bond length and confirmed this view of the changes in the potentials [13, 14] More recent ab initio molecular dynamics studies of ice also produce the observed behaviour This lack of change in O-H bond length with pressure appears to be a general feature in the 0-15 GPa range: it is also observed in ammonia [20], sodium deuteroxide [21], magnesium deuteroxide [22] and cobalt deuteroxide [23] 4'1 Ice X ~ The experimental observation of symmetric ice X has been an important goal since it was first postulated by Ubbelohode in 1949 [24] The search for ice X has led to extensive revisions of the ice phase diagram in the very high pressure region throughout the 1990's Pruzan et al [25] discovered that the transition temperature of the H-bond ordering transition from ice VII to ice VIII (273 K from 2-12 GPa) decreases with increasing pressure and that at ~ 60GPa (70 GPa in D2O) it reaches OK This removed an apparent anomaly since the behaviour of this transition was very different from that observed for other H-bond ordering transitions In 1996 IR studies by Goncharov et al [5] and Aoki et al [26] reported the first evidence of a symmetrisation transition at ~ 75 GPa The manifestation of the transition appeared more complex than previously thought and there has been some dispute as to where the transition occurs (and as to what structurally constitutes ice X); it was clear that a major change in ice begins at this pressure and that the transition to ice X occurs somewhere in the range 75–110 GPa Ab initio modelling by Benoit et al [27] also showed a symmetrisation transition starting at similar pressures where the volume explored by the proton increases as the result of 362 J S LOVEDAY quantum effects This study found an intermediate state where the volume explored by the proton is increased by quantum effects which exist up to ~ 120 GPa with a fully formed ice X above this pressure Subsequent classical modelling by Bernasconi et al was able to reproduce the experimental IR data As a result, it appears that symmetrisation occurred progressively in the range 65–110GPa [28] 4'2 Disorder in ice VII – These revisions of the phase diagram have established the importance of proton-disordered ice VII In addition to dominating the phase diagram at high pressures, it is the phase which transforms into ice X The nature of the disorder is, however, not clear The simple model of ice VII gives an O-D distance that is 0.05 A shorter than that found in ordered ice VIII [29] Such a change cannot be real (it would liberate enough energy to melt the sample) and so it has been assumed that the oxygen atoms were multi-site disordered However, the model proposed by Kuhs et al [29] —O displacement along the cubic (100) directions— overcorrected the O-D distance by as much as 50% More recent studies [30] based on comparison of the atomic displacement (thermal) parameters in ices VII and VIII showed that displacements along (111) gave more plausible internal molecular geometries Such displacements imply that ice VII has two different H-bond lengths ~ 0.1 A longer and shorter than those of ice VIII and that this significant difference is pressure independent up to at least 20 GPa This raises the question as to how such a mixed network will symmeterise (a question that remains to be addressed) The work also raises the question as to what the vibrational spectrum is probing A simple view is that two H-bond lengths would imply a split O-H stretch peak which is not observed even in dilute H in D2O experiments which probe uncoupled O-H vibrations [17] This suggests that the simple view of a direct correlation between H-bond length and O-H stretch frequency may be incorrect This unexpected disorder model also raises the question as to whether the disorder of the oxygen atoms is driven by repulsive interactions between the two H-bond networks [30] 4'3 Beyond ice X – Two recent studies suggest that ice will continue to present challenges beyond ice X Single-crystal X-ray studies of ice VII by Loubyere et al [31] revealed that the structure has an incommensurate superlattice that persists across its entire range of existence and into that of ice X This superlattice is not observed in either X-ray or neutron powder diffraction studies and has been postulated as some kind of partial ordering —a proposal which awaits detailed study Loubeyre et al also found evidence of a possible further structural transition at 150 GPa where Goncharov et al [5] also postulated a transition on the basis of a mode crossing (Fermi resonance) Ab initio molecular-dynamics studies by Cavazonni et al [32] explored the behaviour of H2O at the high pressures and temperatures found within Uranus and Neptune They found evidence for a dissociation of the molecules and protonic conduction that may be the source of the magnetic fields of these planets HYDROGEN BONDING AT HIGH PRESSURE 363 Fig - The ordered structure of ammonia phase IV [20] — Other ices The hydrides of non-metallic elements are classed as ices; water ice is the most studied of this class Studies of other systems provide a means to explore the effect of changing hydrogen bond strength and H-bond geometry 5'1 Ammonia - Ammonia forms weaker hydrogen bonds than water and has an unbalanced geometry in that it has three donor H atoms and only one lone pair to accept H-bonds The high pressure phase diagram was explored by Gauthier et al [33] They found the face-centred cubic phase transformed into phase IV at GPa with a further transition at 12 GPa and then postulated symmetrisation at 60 GPa Otto et al [34] in X-ray studies found a hexagonal close-packed nitrogen arrangement between and at least 30 GPa As a result, it was assumed that like the low-pressure solid phases II and III, phase IV and possibly phase V had rotationally disordered molecules However, neutron diffraction studies showed ammonia IV to be orthorhombic with the ordered arrangement shown in fig [20] Surprisingly, the arrangement has a bifurcated hydrogen bond in which one hydrogen atom forms bonds to two nitrogen atoms Ab initio molecular-dynamics studies by Cavazzoni et al [32] found this structure to be stable to above 100 GPa and, like ice VII, to become a protonic conductor at high temperatures and pressures 5"2 Hydrogen sulphide - Hydrogen sulphide has the same internal molecular geometry as ice but much weaker hydrogen bonding; its ambient pressure structures not show evidence of hydrogen bonds [35] High pressure spectroscopy reveals the vibron softening characteristic of hydrogen bonding [36] and at the highest pressures a blackening that suggests that metallisation occurs at 96 GPa [37] X-ray diffraction studies at ambient temperature reveal transitions at GPa, 11 GPa and 27 GPa, and that metallisation may 364 J S LOVEDAY be the result of short S-S contacts which are not H-bond contacts [38,39] The relationship between the primitive cubic phases II and I' is also of relevance to H-bonding Both have related space groups but, while the ambient pressure phase II has a face-centred cubic sulphur arrangement [35], the sulphur atoms in phase I' are displaced by 0.1 A from fcc sites [38] Neutron diffraction studies [40] revealed that phase I' has a toroidal deuterium arrangement like phase II but that it is more ordered, so that the maxima in the D density point towards six of the twelve nearest-neighbour atoms The displacement of the sulphur atoms from fee sites reduces the S • • • S distance for six neighbours and lengthens it for the other six This arrangement suggests the onset of H-bonding in phase I' and the sharp transition from phase II to I' found at 245 K and 4.5 GPa can be attributed to the onset of H-bonding Modelling studies by Rousseau et al also found a similar behaviour [41] They were not able to reproduce phase I' but found the phase I to IV transition to be a progressive ordering driven by H-bonding [41] Fujhisa and co-workers [42] have recently found new phases in what had been assumed to be the stability field of phase IV below 10 GPa at low temperatures These phases may also reflect the onset of H-bonding — Hydroxyl H-bonds Hydroxyl H-bonds are significantly different from their molecular analogues They are generally weaker and more prone to bifurcation Such bonds are important to the problem of water in the Earth's mantle in addition to their fundamental interest 6"1 Alkali hydroxides - Potassium and sodium hydroxides sit on the boundary of hydrogen bonding KOH exhibits hydrogen bonding that strengthens with increasing pressure NaOH is only H-bonded at low temperatures [43] and spectroscopic studies show that the transition to phase IV at high pressure reverses the softening of vibron [44] Neutron diffraction shows that phase IV has a bifurcated H-bond and it appears that the bifurcation accounts for the lack of softening of the vibron [21] 6"2 Brucite-structured hydroxides - The brucite-structured hydroxides are a model system for H-bonding in hydroxyl-containing systems They have layered structures where the dominant interactions between the metal-oxygen layers are the H-bond interaction and repulsive interactions between the hydrogen atoms [23] Mg(OH)2, brucite, shows a softening of the vibron with pressure indicating a strengthening of the hydrogen bonding [45, 46] Parise et al in neutron diffraction studies found an intriguing change in the disorder of the H(D) atoms [22] The H(D) atoms disordered over three sites around a threefold axis As the pressure is increased in brucite the displacement of H(D) from the threefold axis increases Similar behaviour is observed in Mn(OD) , Ni(OD) and Co(OD)2 [47] Raman and IR studies of Co(OH)2 revealed that the vibron undergoes dramatic broadening at ~ 11 GPa [48] This broadening is very similar to that observed in Ca(OH)2 which undergoes pressure amorphisation [45] However, Co(OH)2 remains crystalline in X-ray studies [48] As a result, Nyugen [48] et al proposed that in Co(OH)2 only the H-sublattice amorphises However, Parise et al [23] showed from neutron data collected HYDROGEN BONDING AT HIGH PRESSURE 365 from Co(OD)2 that the occupancy of the D-site remained fully occupied and that sublattice amorphisation did not occur up to at least 16 GPa A detailed examination of the D-site disorder and the packing of the D layer suggested that the optical anomaly could be explained instead by changes in the symmetry of the D-site The need to maintain a D • • • D distance of more the 1.8 A forces the D-atoms to occupy general positions This means that the D-atoms have a wide range of different bonding environments that could account for the broadening of the vibron Recent ab initio modelling of Ca(OH)2 produces a similar sort of disorder distribution [49] — Clathrate hydrates and other water-gas mixtures The behaviour of mixtures provides a very valuable extension to studies of singlecomponent systems Mixtures provide a means to probe phenomena like repulsive interactions and mixed H-bonds that are not so readily accessible and mixtures may yield analogous structures that provide insight into the parent single-component systems A classical water-gas mixture is the clathrate-hydrate where the guest gas molecules sit in the centre of cages formed of H-bonded water molecules; the whole structure is stabilised by water-guest repulsions High pressure studies have revealed a number of other types of mixture 7'1 Filled-ice clathrates – Small species like hydrogen and helium are too small to form cage clathrates and the discovery that helium forms a hydrate structure based on that of ice II caused considerable surprise [50] Vos et al [51] explored the hydrogen water system and found an ice II related hydrate which appeared to be similar to helium hydrate and above 2.7GPa a second hydrate This second hydrate has a 1:1 water:hydrogen ratio and a water network like that of ice Ic with hydrogen sitting in voids in the network This structure is related to that of ice VII, which consists of two interpenetrating ice Ic networks H2 • H2O is approximately twice as compressible as ice VII and spectroscopic studies suggest that the network of H-bonds may undergo symmetrisation at ~ 30 GPa [52] Although these mixtures are called clathrates, their structures not have cages and resemble ice structures very closely It is thus more informative to refer to them as filled ice clathrates or hydrates 7'2 Cage clathrates – The high pressure behaviour of cage clathrates provides important information on hydrophobic interactions In the cases of simple gas hydrates like those of methane, nitrogen, oxygen and carbon dioxide it is also directly relevant to modelling of the Earth and other planets They have been extensively studied in the 0–1 GPa range; phase transitions have been reported in argon, methane and nitrogen hydrates [53–56] However, very little work had been carried out at pressures above this and the expectation was that they would decompose into guest and ice at to GPa [54] In the past two years this view has been overturned Initial indications of high pressure gas hydrates came from Raman studies of argon hydrate which showed hydrate phases stable to GPa [56] X-ray and neutron diffraction studies of methane hydrate revealed two new phases [57] The first is a hexagonal hydrate stable between 0.8 GPa and 1.9 GPa with 674 ELENCO DEI PARTECIPANTI Lucia CIABINI Universita di Firenze Dipartimento di Chimica P.zza Puccini 26 50100 FIRENZE Italy Fax: ++39 055 224072 ciabini@lens.unifi.it Alberta CONGEDUTI Universita di Roma "La Sapienza" Dipartimento di Fisica P.le Aldo Moro 00185 ROMA Italy Tel.: ++39 06 49913502 Fax: ++39 06 4463158 congedut@caspur.it Margherita CITRONI Universita di Firenze Dipartimento di Chimica Via Dolfi 50129 FIRENZE Italy Tel.: ++39 055 471968 Fax: ++39 055 224072 margherita@lens.unifi.it Regis DEBORD Laboratoire de Physique des Milieux Condenses Place Jussieu PARIS 75252 France Tel.: ++33 01 44 27 44 64 Fax: ++33 01 44 27 44 69 rd@pmc.jussieu.fr Matteo COCOCCIONI SISSA - ISAS International School for Advanced Studies Via Beirut 2-4 Via 34014 TRIESTE Italy Tel.: ++39 040 3787429 Fax: ++39 040 3787528 cococ@sissa.it Simone DE PANFILIS Universita di Camerino Dipartimento di Matematica e Fisica Madonna delle Carceri 62032 CAMERINO MC TeL: ++39 0737 402535 Fax: ++39 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3555 Fax: ++81 52 789 3013 okuchi@eps.nagoya-u.ac.jp Marcus ORIGLIERI Department of Geosciences University of Arizona Gould-Simpson Building 1040 E Fourth Street TUCSON, AZ 85721-0077 USA Tel.: ++1 520 626 8092/275 0829 Fax: ++1 520 621 2672 marcus@geo.arizona.edu Sergey OVSYANNIKOV Institute fo Metals Physics 620219 EKATERINBURG GSP-170 Russia Tel.: ++7 3432 499045 Fax: ++7 3432 745244 vladimir.v@imp.uran.ru ELENCO DEI PARTECIPANTI Reed PATTERSON University of Alabama at Birmingham 310 Campbell Hall Department of Physics 1300 University Boulevard BIRMINGHAM, AL 35294–1170 USA Tel: ++1 205 934 8260 Fax: ++1 205 934 8042 jrp@lorentz.phy.uab.edu Ivana RADISAVLJEVIC Institute of Nuclear Sciencec VINCA Lab 011, P.O Box 522 11001 BELGRADE Yugoslavia Fax: ++381 11 453681 iva@rt270.vin.bg.ac.yu Chrystele SANLOUP Carnegie Institution of Washington Geophysical Laboratory 5251 Broad Branch Road, NW WASHINGTON, DC 20015 USA Tel.: ++1 202 478 8925 Fax ++1 202 478 8901 sanloup@gl.ciw.edu Thomas 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olga.shebanova@geo.uu.se Manuela Elena STIR Rostock University Physics Department August-Babel-Str 55 18055 ROSTOCK Germany Tel: ++49 381 498 2877 Fax: ++49 381 498 1726 stir@physicl.uni-rostock.de Dharmbir SINGH M.M Engg College AMBALA India Tel: ++91 731 75841/42/43 Fax: ++ 91 731 75793 dharmbir@yahoo.com Akio SUZUKI Bayerisches Geoinstitut Universitat Bayreut 95440 BAYREUT Germany Tel: ++49 921 553712 Fax: ++49 921 553769 akio.suzuki@uni-bayreuth.de 680 Paul TANGNEY SISSA International School for Advanced Studies Via Beirut 2-4 34100 TRIESTE Italy Tel.: ++01 609 2580494 Fax: ++01 609 258 6878 tangney@sissa.it Leonardo TASSINI Universita di Firenze Dipartimento di Fisica Largo E Fermi 50125 FIRENZE Italy Tel.: ++39 055 644162 tassinileonardo@hotmail.com Chris A TULK Oak Ridge National Laboratory Argonne National Lab 9700 S Cass Ave ARGONNE, IL USA Tel.: ++1 630 252 9881 Fax: ++1 630 252 4163 ctulk@anl.gov Feodor YEL'KIN Institute for High Pressure Physics Russian Academy of Sciences 142190, Troitsk MOSCOW Region Russia Tel.: ++7 095 334 0803 Fax: ++7 095 334 0012 fse@hppi.troitsk.ru ELENCO DEI PARTECIPANTI Tony YU State University of New York at Stony Brook 1341 Stony Brook Road STONY BROOK, NY 11794-2100 USA Tel.: ++1 631 246 6076 tony.yu@sunysb.edu Observers Chang-Qing JIN Institute of Physics Chinese Academy of Sciences P.O Box 603 BEIJING 100080 China Tel.: ++86 10 82649163 Fax ++86 10 82649531 cqjin@iphy.ac.cn Richard NELMES ISIS Facility Rutherford Appleton Laboratory Chilton, Didcot OXON OX11 0QX UK Tel.: ++44 1235 445285 Fax: ++44 1235 445103 rjn01@isise.rl.ac.uk Suresh C SHARMA Department of Physics, Box 19059 University of Texas at Arlington ARLINGTON, TX 76019 USA Tel: ++1 817 272 2470 Fax: ++1 817 272 3637 sharma@uta.edu ELENCO DEI PARTECIPANTI Pessia SHUKER Nuclear Research Center-NEGEV P.O Box 9001 BEER-SHEVA 84190 Israel Tel: ++972 6567600 Fax: ++972 6568770 pshuker@bgumail.bgu.ac.il 681 Liling SUN Institute of Physics Chinese Academy of Sciences P.O Box 603 BEIJING 100080 China Tel: ++86 10 82649148 Fax ++86 10 82649531 llsun@aphy.iphy.ac.cn This page intentionally left blank PROCEEDINGS OF THE INTERNATIONAL SCHOOL OF PHYSICS «ENRICO FERMI» Course I (1953) Questions relative alla rivelazione delle particelle elementari, particolare riguardo alla radiazione cosmica edited by G PUPPI Course II (1954) Questioni relative alla rivelazione delle particelle elementari, e alle loro interazioni particolare riguardo alle particelle artificialmente prodotte ed accelerate edited by G PUPPI Course XIII (1959) Physics of Plasma: Experiments Techniques edited by H ALFVEN and Course XIV (1960) Ergodic Theories edited by P CALDIROLA Course XV (1960) Nuclear Spectroscopy edited by G RACAH Course III (1955) Questioni di struttura nucleare e dei processi nucleari alle basse energie edited by C SALVETTI Course XVI (1960) Physicomathematical Course IV (1956) Proprieta magnetiche della materia edited by L GIULOTTO Course XVII (1960) Topics of Radiofrequency edited by A GOZZINI Course V (1957) Fisica dello stato solido edited by F FUMI Course XVIII (1960) Physics of Solids (Radiation Damage in Solids) edited by D S BILLINGTON Course VI (1958) Fisica del plasma e relative applicazioni astrofisiche edited by G RIGHINI Course VII (1958) Teoria della informazione edited by E R CAIANIELLO Aspects of Bio- edited by N RASHEVSKY Spectroscopy Course XIX (1961) Cosmic Rays, Solar Particles and Space Research edited by B PETERS Course XX (1961) Evidence for Gravitational Theories edited by C M0LLER Course VIII (1958) Problemi matematici della teoria quantistica delle particelle e dei campi edited by A BORSELLINO Course XXI (1961) Liquid Helium edited by G CARERI Course IX (1958) Fisica dei pioni edited by B TOUSCHEK Course XXII (1961) Semiconductors edited by R A SMITH Course X (1959) Thermodynamics of Irreversible cesses edited by S R DE GROOT Pro- Course XXIII (1961) Nuclear Physics edited by V F WEISSKOPF Course XI (1959) Weak Interactions edited by L A RADICATI Course XXIV (1962) Space Exploration System edited by B Rossi Course XII (1959) Solar Radioastronomy edited by G RIGHINI Course XXV (1962) Advanced Plasma Theory edited by M N ROSENBLUTH and the Solar Course XXVI (1962) Selected Topics on Elementary Particle Physics edited by M CONVERSI Course XXVII (1962) Dispersion and Absorption of Sound by Molecular Processes edited by D SETTE Course XLII (1967) Quantum Optics edited by R J GLAUBER Course XLIII (1968) Processing of Optical Data by Organisms and by Machines edited by W REICHARDT Course XXVIII (1962) Star Evolution edited by L GRATTON Course XLIV (1968) Molecular Beams and Reaction Kinetics edited by CH SCHLIER Course XXIX (1963) Dispersion Relations and their Connection with Causality edited by E P WIGNER Course XLV (1968) Local Quantum Theory edited by R JOST Course XXX (1963) Radiation Dosimetry edited by F W SPIERS and G W REED Course XLVI (1969) Physics with Intersecting Storage Rings edited by B TOUSCHEK Course XXXI (1963) Quantum Electronics and Coherent Light edited by C H TOWNES and P A MILES Course XLVII (1969) General Relativity and Cosmology edited by R K SACHS Course XXXII (1964) Weak Interactions and High-Energy Neutrino Physics edited by T D LEE Course XLVIII (1969) Physics of High Energy Density edited by P CALDIROLA and H KNOEPFEL Course XXXIII (1964) Strong Interactions edited by L W ALVAREZ Course XXXIV (1965) The Optical Properties of Solids edited by J TAUC Course XXXV (1965) High-Energy Astrophysics edited by L GRATTON Course XXXVI (1965) Many-Body Description of Nuclear Structure and Reactions edited by C BLOCH Course XXXVII (1966) Theory of Magnetism in Transition Metals edited by W MARSHALL Course XXXVIII (1966) Interaction of High-Energy Particles with Nuclei edited by T E ERICSON Course IL (1970) Foundations of Quantum Mechanics edited by B D'ESPAGNAT Course L (1970) Mantle and Core in Planetary Physics edited by J COULOMB and M CAPUTO Course LI (1970) Critical Phenomena edited by M S GREEN Course LII (1971) Atomic Structure and Properties of Solids edited by E BURSTEIN Course LIII (1971) Developments and Borderlines of Nuclear Physics edited by H MORINAGA Course LIV (1971) Developments in High-Energy Physics edited by R R GATTO Course XXXIX (1966) Plasma Astrophysics edited by P A STURROCK Course LV (1972) Lattice Dynamics and Forces edited by S CALIFANO Course XL (1967) Nuclear Structure and Nuclear Reactions edited by M JEAN and R A RICCI Course LVI (1972) Experimental Gravitation edited by B BERTOTTI Course XLI (1967) Selected Topics in Particle Physics edited by J STEINBERGER Course LVII (1972) History of 20th Century Physics edited by C WEINER Intermolecular Course LVIII (1973) Dynamics Aspects of Surface Physics edited by F GOODMAN Course LXXII (1977) Problems in the Foundations of Physics edited by G TORALDO DI FRANCIA Course LIX (1973) Local Properties at Phase Transitions edited by K A MULLER and A RIGAMONTI Course LXXIII (1978) Early Solar System Processes and the Present Solar System edited by D LAL Course LX (1973) C*-Algebras and their Applications to Statistical Mechanics and Quantum Field Theory edited by D KASTLER Course LXXIV (1978) Development of High-Power Lasers and their Applications edited by C PELLEGRINI Course LXI (1974) Atomic Structure and Mechanical Properties of Metals edited by G CAGLIOTI Course LXII (1974) Nuclear Spectroscopy and Nuclear Reactions with Heavy Ions edited by H FARAGGI and R A RICCI Course LXIII (1974) New Directions in Physical Acoustics edited by D SETTE Course LXIV (1975) Nonlinear Spectroscopy edited by N BLOEMBERGEN Course LXV (1975) Physics and Astrophysics of Neutron Stars and Black Holes edited by R GIACCONI and R RUFFINI Course LXVI (1975) Health and Medical Physics edited by J BAARLI Course LXVII (1976) Isolated Gravitating Systems in General Relativity edited by J EHLERS Course LXVIII (1976) Metrology and Fundamental Constants edited by A FERRO MILONE, P GIACOMO and S LESCHIUTTA Course LXIX (1976) Elementary Modes of Excitation in Nuclei edited by A BOHR and R A BROGLIA Course LXX (1977) Physics of Magnetic Garnets edited by A PAOLETTI Course LXXI (1977) Weak Interactions edited by M BALDO CEOLIN Course LXXV (1978) Intermolecular Spectroscopy and Dynamical Properties of Dense Systems edited by J VAN KRANENDONK Course LXXVI (1979) Medical Physics edited by J R GREENING Course LXXVII (1979) Nuclear Structure and Heavy-Ion Collisions edited by R A BROGLIA, R A RICCI and C H DASSO Course LXXVIII (1979) Physics of the Earth's Interior edited by A M DZIEWONSKI and E BoSCHI Course LXXIX (1980) From Nuclei to Particles edited by A MOLINARI Course LXXX (1980) Topics in Ocean Physics edited by A R OSBORNE and P MALANOTTE RIZZOLI Course LXXXI (1980) Theory of Fundamental Interactions edited by G COSTA and R R GATTO Course LXXXII (1981) Mechanical and Thermal Behaviour of Metallic Materials edited by G CAGLIOTI and A FERRO MILONE Course LXXXIII (1981) Positrons in Solids edited by W BRANDT and A DUPASQUIER Course LXXXIV (1981) Data Acquisition in High-Energy Physics edited by G BOLOGNA and M VINCELLI Course LXXXV (1982) Earhquakes: Observation, Theory and Interpretation edited by H KANAMORI and E BOSCHI Course LXXXVI (1982) Gamma Cosmology edited by F MELCHIORRI and R RUFFINI Course LXXXVII (1982) Nuclear Structure and Heavy-Ion Dynamics edited by L MORETTO and R A Ricci Course LXXXVIII (1983) Turbulence and Predictability in Geophysical Fluid Dynamics and Climate Dynamics edited by M GHIL, R BENZI and G PARIsi Course LXXXIX (1983) Highlights of Condensed-Matter Theory edited by F BASSANI, F FUMI and M P Tosi Course XC (1983) Physics of Amphiphphies Micelles, Vesicles and Microemulsions edited by V DEGIORGIO and M CORTI Course XCI (1984) From Nuclei to Stars edited by A MOLINARI and R A RICCI Course XCII (1984) Elementary Particles edited by N CABIBBO Course XCIII (1984) Frontiers in Physical Acoustics edited by D SETTE Course XCIV (1984) Theory of Reliability edited by A SERRA and R E BARLOW Course XCV (1985) Solar-Terrestrial Relationships and the Earth Environment in the Last Millennia edited by G CINI CASTAGNOLI Course C (1986) The Physics of NMR Spectroscopy Biology and Medicine edited by B MARAVIGLIA in Course CI (1986) Evolution of Interstellar Dust and Related Topics edited by A BONETTI and J M GREENBERG Course CII (1986) Accelerated Life Testing and Opinions in Reliability edited by C A CLAROTTI Experts Course CIII (1987) Trends in Nuclear Physics edited by P KIENLE, R A RICCI and A RUBBINO Course CIV (1987) Frontiers and Borderlines in Many-Particle Physics edited by R A BROGLIA and J R SCHRIEFFER Course CV (1987) Confrontation between Theories and Observations in Cosmology: Present Status and Future Programmes edited by J AUDOUZE and F MELCHIORRI Course CVI (1988) Current Trends in the Physics of Materials edited by G F CHIAROTTI, F FUMI and M Tosi Course CVII (1988) The Chemical Physics of Atomic and Molecular Clusters edited by G SCOLES Course XCVI (1985) Excited-State Spectroscopy in Solids edited by U M GRASSANO and N TERZI Course CVIII (1988) Photoemission and Absorption Spectroscopy of Solids and Interfaces with Synchrotron Radiation edited by M CAMPAGNA and R ROSEI Course XCVII (1985) Molecular-Dynamics Simulations of Statistical-Mechanical Systems edited by G Ciccorn and W G HOOVER Course CLX (1988) Nonlinear Topics in Ocean Physics edited by A R OSBORNE Course XCVIII (1985) The Evolution of Small Bodies in the Solar System edited by M FULCHIGNONI and L KRE- Course CX (1989) Metrology at the Frontiers of Physics and Technology edited by L CROVINI and T J QUINN SAK Course XCIX (1986) Synergetics and Dynamic Instabilities edited by G CAGLIOTI and H HAKEN Course CXI (1989) Solid-State Astrophysics edited by E BUSSOLETTI and G STRAZZULLA Course CXII (1989) Nuclear Collisions from the Mean-Field into the Fragmentation Regime edited by C DETEAZ and P KIENLE Course CXIII (1989) High-Pressure Equation of State: Theory and Applications edited by S ELIEZER and R A RICCI Course CXIV (1990) Industrial and Technological Applications of Neutrons edited by M FONTANA and F RUSTICHELLI Course CXV (1990) The Use of EOS for Studies of Atmospheric Physics edited by J C GILLE and G VISCONTI Course CXVI (1990) Status and Perspectives of Nuclear Energy: Fission and Fusion edited by R A RICCI, C SALVETTI and E SlNDONI Course CXVII (1991) Semiconductor Superlattices and Interfaces edited by A STELLA Course CXVIII (1991) Laser Manipolation of Atoms and Ions edited by E ABIMONDO, W D PHILLIPS and F STRUMIA Course CXIX (1991) Quantum Chaos edited by G CASATI, I GUARNERI and U SMILANSKY Course CXX (1992) Frontiers in Laser Spectroscopy edited by T W HANSCH and M INGUSCIO Course CXXI (1992) Perspectives in Many-Particle Physics edited by R A BROGLIA, J R SCHRIEFFER and P F BORTIGNON Course CXXII (1992) Galaxy Formation edited by J SILK and N VITTORIO Course CXXIII (1992) Nuclear Magnetic Double Resonance edited by B MARAVIGLIA Course CXXIV (1993) Diagnostic Tools in Atmospheric Physics edited by G.FIOCCOand G VISCONTI Course CXXV (1993) Positron Spectroscopy of Solids edited by A DUPASQUIER and A P MILLS jr Course CXXVI (1993) Nonlinear Optical Materials: Principles and Applications edited by V DEGIORGIO and C FLYTZANIS Course CXXVII (1994) Quantum Groups and their Applications in Physics edited by L CASTELLANI and J WESS Course CXXVIII (1994) Biomedical Applications of Synchrotron Radiation edited by E BURATTINI and A BALERNA Course CXXIX (*) (1994) Observation, Prediction and Simulation of Phase Transitions in Complex Fluids edited by M BAUS, L F RULL and J.-P RYCKAERT Course CXXX (1995) Selected Topics in Nonperturbative QCD edited by A Di GIACOMO and D DIAKONOV Course CXXXI (1995) , Coherent and Collective Interactions of Particles and Radiation Beams edited by A ASPECT, W BARLETTA and R BONIFACIO Course CXXXII (1995) Dark matter in the Universe edited by S BONOMETTO and J PRIMACK Course CXXXIII (1996) Past and Present Variability of the SolarTerrestrial System: Measurement, Data Analysis and Theoretical Models edited by G CINI CASTAGNOLI and A PROVENZALE Course CXXXIV (1996) The Physics of Complex Systems edited by F MALLAMACE and H E STANLEY Course CXXXV (1996) The Physics of Diamond edited by A PAOLETTI and A TUCCIARONE Course CXXXVI (1997) Models and Phenomenology for Conventional and High-Temperature Superconductivity edited by G IADONISI, J R SCHRIEFFER and M L CHIOFALO (*) This course belongs to the NATO ASI Series C, Vol 460 (Kluwer Academic Publishers) Course CXXXVII (1997) Heavy Flavour Physics: a Probe of Nature's Grand Design edited by I BIGI and L MORONI Course CXLII (1999) Plasma Astrophysics edited by B COPPI, A FERRARI and E SINDONI Course CXXXVIII (1997) Unfolding the Matter of Nuclei edited by A MOLINARI and R A RICCI Course CXLIII (1999) New Directions in Quantum Chaos edited by G CASATI, I GUARNERI and U SMILANSKY Course CXXXIX (1998) Magnetic Resonance and Brain Function: Approaches from Physics edited by B MARAVIGLIA Course CXLIV (2000) Nanometer Scale Science and Technology edited by M ALLEGRINI, N GARCIA and MARTI Course CXL (1998) Bose-Einstein Condensation in Atomic Gases edited by M INGUSCIO, S STRINGARI and C E WlEMAN Course CXLI (1998) Silicon-Based Microphotonics: From Basics to Applications edited by BISI, S U CAMPISANO, L PAVESI and F PRIOLO Course CXLV (2000) Protein Folding, Evolution and Design edited by R A BROGLLA, E I SHAKHNOVICH and G TIANA Course CXLVI (2000) Recent Advances in Metrology and Fundamental Constants edited by T J QUINN, S LESCHIUTTA and P TAVELLA ... estimates of the variation of the O-H bond length with pressure shown in fig change in the bond length implies that the softening of the vibron can be interpreted as a changes of the curvature of the. .. indicating a weakening of the (covalent) molecular bond and a strengthening of the hydrogen bond [17] In the absence of direct measurements, estimates were made of the extension of the covalent O-H... that as the H-bond compresses and the acceptor atom moves closer to the hydrogen the attraction of H by the acceptor causes the covalent O-H bond to lengthen, and this lengthening weakens the O-H