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Spectroscopy and relaxation of molecular liquids
Spectrochimica Acra, Pergamon Press Ltd.
Vol. 49A. No. 11. pp. 1685-1686. Printed inGrealBritain
1993
BOOK REVIEWS NUCLEAR AND ELECTRON RELAXATION: THE MAGNETIC NUCLEUS - UNPAIRED ELECTRON COUPLING IN SOLUTION, by L. BANCI, I. BERTINI and C. LUCHINAT. VCH, Weinheim (1991). 208+xvi pp. Price DM 118.00. ISBN 3-527-28306-4. This book is about nuclear spin relaxation in paramagnetic systems and is addressed to those whore background lies in NMR. The authors have themselves made many useful contributions to the understanding of these systems and discussion of them has been part of the programme of successive Chianti workshops on magnetic resonance, which the authors have organized and run since 1984. Their experiences of research in the field and of teaching about it at the workshops are focussed into this book. The philosophy is that to understand nuclear spin relaxation in paramagnetic systems one also needs to understand electron spin relaxation and given that the essential physics is common to both sorts of spin then the construction of a unified treatment is logical and desirable. The opening chapter sets out some basic ideas about relaxation and background material on the spinHamiltonian for paramagnetic species. An idiosyncratic feature is a level diagram for an S = 112, I = 112 system in a magnetic field for the case of a negative nuclear magnetogyric ratio. This is not, to my mind, the obvious case to choose for illustrate purposes: the dia ram is not useful for ‘H, r3C, lsF or “P although, to bc fair, it is for about 16 less common nuclei (including BHe and ‘“Xe!). Relaxation times T,, Tr and TLCare defined in Chap. 2, where the Bloch equations are introduced, and experimental methods for their measurement, mainly by pulse techniques, are described in Chap. 3. The mechanisms of electron spin relaxation in dilute systems, for both solid and liquid phases, are described in Chap. 4, while the mirror image, nuclear relaxation in paramagnetic systems, is discussed in Chap. 5, where several fairly complex formulae for the relaxation times resulting from various mechanisms are quoted. The final two chapters deal with more specific areas. The field dependence of proton relaxation rates, defined as relaxivities, T;r’ImM, for aquated Cu(II), Co(II), Ni(II), and Mn(I1) ions are described in Chap. 6, while high spin systems, moving from dimeric systems towards clusters, are the subject of Chap. 7. Systems of this sort are, of course, not uncommon in species of biological significance. The book ends with a series of appendices in which the derivations of some useful theoretical results, and their applications, are discussed. The book is aimed at postgraduate and postdoctoral researchers who have a background in NMR and who wish to move into the study of paramagnetic species. The crucial question for the reviewer is to try to discern how useful this target audience will find it. This is not an easy matter for this particular reviewer whose background is in EPR and who may have a different perspective on magnetic resonance than some of the target readership. It sometimes seems to me that some users of NMR know all the right words but do not have very secure physical insight: if such people do indeed exist then their shortcoming may be usefully remedied to some extent by parts of this book. On the other hand, I feel that people seeking to really get to grips with spin relaxation theory may find here only a partial bridge to the literature. For example, modem magnetic resonance theory is most powerfully couched in the density matrix formalism, but this is not discussed at all. To summarize, the authors have tried to achieve a balance between a purely physical description of spin relaxation and a more theoretical one. This is a difficult balance to strike in a short space but I think the authors have achieved some success so that members of the target readership, be they of experimental or theoretical bent, will find something of value. Not least, the essential unity of the physics underlying all spin relaxation processes, something which is not perhaps as widely appreciated as it ought to be, is underlined by this book. Department of Chemistry lJniversi@ of Sheffield Shefield S3 7HF U.K.
N. M. ATHERTON
SPECTROSCOPY AND RELAXATION OF MOLECULAR J. YARWOOD). Elsevier, Amsterdam (1991). 544 pp.
LIQUIDS (Edited by D.
STEELE
and
In Spectroscopy and Relaxation of Molecular Liquids, introductions/reviews written by specialists in different techniques are collected. The book is aimed at graduate students and scientists new to the field of relaxation in liquids. It was not intended as an up-to-date review-references are mostly to work before 1987 and the latest reference is to 1990. Some chapters do not proceed beyond 1983 and 1985. From the experimental point of view the emphasis is on IR, Raman, and microwave spectroscopy. Still, light scattering, neutron scattering, NMR and molecular dynamics are introduced. Theoretical introductions treat molecular reorientation and collision-induced processes. It is a useful book that any laboratory involved in research and or teaching in the field of liquid state spectroscopy will need to have. It is also a badly printed book to the point of unpleasantness. The large number 1685
1686
Book Reviews
of typos undoubtedly reflects the lack of time at the disposal of people involved in scientific research these days, and may pose some problems for the uninitiated. The introduction to the theory of IR and Raman band shapes is adequate and useful experimental examples are given. The presentation is from the point of view of the molecular spectroscopist-there is no explicit connection with statistical physics and linear response theory. Rotations are represented with Cartesian matrices instead of using the concise irreducible tensor formalism which is used in the next chapter on molecular reorientation. This excellent discussion (Chap. 3) is very short for students; this is especially regretted for the discussion of the generalized Langevin equation and of the “cumulant method”. Chapter 4 on collision-induced process starts with the application of correlation functions to microwave spectroscopy, IR, Raman and light scattering. It is regrettable that a similar but more extended presentation including neutron scattering and nuclear magnetic relaxation was not included in Chap. 2 of this book. The importance of recognizing collision-induced processes is rightly stressed and it is concluded that time-scale separation may be expected to work only in dense fluids where reorientational motion is appreciably hindered. The chapter on microwave spectroscopy and IR presents an excellent review of the problems and pitfalls awaiting the worker in these spectral regions. It is further clearly demonstated that the interpretation is by no means simpler than the collection of “clean” experimental data. A wide variety of low frequency molecular processes contribute: one directly monitors the “bath” instead of looking at something, e.g. a spin system, which is relaxed by a weak coupling to the bath. The perennial internal field problem is mentioned. The chapter on “IR and Raman studies on molecular motion in liquids” contains many useful practical units and caveats for the experimenter. The space used for (again) explaining the relevant correlation functions could have been used differently if a unified presentation had been agreed upon which could have been presented more extensively in Chap. 2. From this review it is clear that IR and Raman studies of molecular dynamics have been confined to simple, small molecules: one needs isolated bonds. Important results on orientational and vibrational relaxation have been obtained. Detailed quantitative testing of motional models is still at the limit of the method however. Students will have difficulties with the excellent but over condensed (30 pages!) discussion of light scattering. The isotropic Rayleigh-Brillouin scattering is clearly presented in terms of the thermal diffusion, sound waves and possible structural relaxation. The expected effect of interaction induced change of the polarixability is discussed. The basic concepts for Depolarized Rayleigh Scattering are introduced for linear molecules and experimental results are discussed with CO* as an example. The chapter ends with a warning that no reliable separation procedure has been developed for the orientational- and interaction-induced features. Neutron scattering with an emphasis on incoherent scattering is introduced in an admirably clear and efficient way. The scattering laws for translational and rotational diffusion are explained clearly and the importance of the elastic incoherent structure factor is stressed. As an example, the molecular motion in liquid furan is discussed: translational and rotational diffusion coefficients are obtained. A confrontation with the possibilities of NMR is sorely missed here. The basic NMR principles are condensed to a level precluding insight into the possibilities of this powerful technique. Only simple exponential decay is mentioned and T;’ is introduced as being proportional to the spectral density at the Larmor frequency. Explicit expressions later on in this chapter will therefore elude the beginner. Motional models are discussed adequately although a curious emphasis is put on a “model free” approach which by its very nature cannot be very informative on molecular motion. In the last chapter classical MD simulations are introduced and the simulation of dielectric, IR, Raman and light scattering is discussed. Reading this chapter may give students, among other things, a feeling for the molecular features in the correlation functions and for spectral densities obtained with spectroscopic techniques. To conclude, the editors and contributors certainly approximate their stated goal by collecting a wide range of information on different techiques in this book. Physical and Macromolecular Chemistry Leiden University Gorlaeus Laboratories Einsteinweg 55 2233 CC Leiden The Netherlands
J. C.
h3’TE
Vol. 49A. No. 11. pp. 1685-1686. Printed inGrealBritain
1993
BOOK REVIEWS NUCLEAR AND ELECTRON RELAXATION: THE MAGNETIC NUCLEUS - UNPAIRED ELECTRON COUPLING IN SOLUTION, by L. BANCI, I. BERTINI and C. LUCHINAT. VCH, Weinheim (1991). 208+xvi pp. Price DM 118.00. ISBN 3-527-28306-4. This book is about nuclear spin relaxation in paramagnetic systems and is addressed to those whore background lies in NMR. The authors have themselves made many useful contributions to the understanding of these systems and discussion of them has been part of the programme of successive Chianti workshops on magnetic resonance, which the authors have organized and run since 1984. Their experiences of research in the field and of teaching about it at the workshops are focussed into this book. The philosophy is that to understand nuclear spin relaxation in paramagnetic systems one also needs to understand electron spin relaxation and given that the essential physics is common to both sorts of spin then the construction of a unified treatment is logical and desirable. The opening chapter sets out some basic ideas about relaxation and background material on the spinHamiltonian for paramagnetic species. An idiosyncratic feature is a level diagram for an S = 112, I = 112 system in a magnetic field for the case of a negative nuclear magnetogyric ratio. This is not, to my mind, the obvious case to choose for illustrate purposes: the dia ram is not useful for ‘H, r3C, lsF or “P although, to bc fair, it is for about 16 less common nuclei (including BHe and ‘“Xe!). Relaxation times T,, Tr and TLCare defined in Chap. 2, where the Bloch equations are introduced, and experimental methods for their measurement, mainly by pulse techniques, are described in Chap. 3. The mechanisms of electron spin relaxation in dilute systems, for both solid and liquid phases, are described in Chap. 4, while the mirror image, nuclear relaxation in paramagnetic systems, is discussed in Chap. 5, where several fairly complex formulae for the relaxation times resulting from various mechanisms are quoted. The final two chapters deal with more specific areas. The field dependence of proton relaxation rates, defined as relaxivities, T;r’ImM, for aquated Cu(II), Co(II), Ni(II), and Mn(I1) ions are described in Chap. 6, while high spin systems, moving from dimeric systems towards clusters, are the subject of Chap. 7. Systems of this sort are, of course, not uncommon in species of biological significance. The book ends with a series of appendices in which the derivations of some useful theoretical results, and their applications, are discussed. The book is aimed at postgraduate and postdoctoral researchers who have a background in NMR and who wish to move into the study of paramagnetic species. The crucial question for the reviewer is to try to discern how useful this target audience will find it. This is not an easy matter for this particular reviewer whose background is in EPR and who may have a different perspective on magnetic resonance than some of the target readership. It sometimes seems to me that some users of NMR know all the right words but do not have very secure physical insight: if such people do indeed exist then their shortcoming may be usefully remedied to some extent by parts of this book. On the other hand, I feel that people seeking to really get to grips with spin relaxation theory may find here only a partial bridge to the literature. For example, modem magnetic resonance theory is most powerfully couched in the density matrix formalism, but this is not discussed at all. To summarize, the authors have tried to achieve a balance between a purely physical description of spin relaxation and a more theoretical one. This is a difficult balance to strike in a short space but I think the authors have achieved some success so that members of the target readership, be they of experimental or theoretical bent, will find something of value. Not least, the essential unity of the physics underlying all spin relaxation processes, something which is not perhaps as widely appreciated as it ought to be, is underlined by this book. Department of Chemistry lJniversi@ of Sheffield Shefield S3 7HF U.K.
N. M. ATHERTON
SPECTROSCOPY AND RELAXATION OF MOLECULAR J. YARWOOD). Elsevier, Amsterdam (1991). 544 pp.
LIQUIDS (Edited by D.
STEELE
and
In Spectroscopy and Relaxation of Molecular Liquids, introductions/reviews written by specialists in different techniques are collected. The book is aimed at graduate students and scientists new to the field of relaxation in liquids. It was not intended as an up-to-date review-references are mostly to work before 1987 and the latest reference is to 1990. Some chapters do not proceed beyond 1983 and 1985. From the experimental point of view the emphasis is on IR, Raman, and microwave spectroscopy. Still, light scattering, neutron scattering, NMR and molecular dynamics are introduced. Theoretical introductions treat molecular reorientation and collision-induced processes. It is a useful book that any laboratory involved in research and or teaching in the field of liquid state spectroscopy will need to have. It is also a badly printed book to the point of unpleasantness. The large number 1685
1686
Book Reviews
of typos undoubtedly reflects the lack of time at the disposal of people involved in scientific research these days, and may pose some problems for the uninitiated. The introduction to the theory of IR and Raman band shapes is adequate and useful experimental examples are given. The presentation is from the point of view of the molecular spectroscopist-there is no explicit connection with statistical physics and linear response theory. Rotations are represented with Cartesian matrices instead of using the concise irreducible tensor formalism which is used in the next chapter on molecular reorientation. This excellent discussion (Chap. 3) is very short for students; this is especially regretted for the discussion of the generalized Langevin equation and of the “cumulant method”. Chapter 4 on collision-induced process starts with the application of correlation functions to microwave spectroscopy, IR, Raman and light scattering. It is regrettable that a similar but more extended presentation including neutron scattering and nuclear magnetic relaxation was not included in Chap. 2 of this book. The importance of recognizing collision-induced processes is rightly stressed and it is concluded that time-scale separation may be expected to work only in dense fluids where reorientational motion is appreciably hindered. The chapter on microwave spectroscopy and IR presents an excellent review of the problems and pitfalls awaiting the worker in these spectral regions. It is further clearly demonstated that the interpretation is by no means simpler than the collection of “clean” experimental data. A wide variety of low frequency molecular processes contribute: one directly monitors the “bath” instead of looking at something, e.g. a spin system, which is relaxed by a weak coupling to the bath. The perennial internal field problem is mentioned. The chapter on “IR and Raman studies on molecular motion in liquids” contains many useful practical units and caveats for the experimenter. The space used for (again) explaining the relevant correlation functions could have been used differently if a unified presentation had been agreed upon which could have been presented more extensively in Chap. 2. From this review it is clear that IR and Raman studies of molecular dynamics have been confined to simple, small molecules: one needs isolated bonds. Important results on orientational and vibrational relaxation have been obtained. Detailed quantitative testing of motional models is still at the limit of the method however. Students will have difficulties with the excellent but over condensed (30 pages!) discussion of light scattering. The isotropic Rayleigh-Brillouin scattering is clearly presented in terms of the thermal diffusion, sound waves and possible structural relaxation. The expected effect of interaction induced change of the polarixability is discussed. The basic concepts for Depolarized Rayleigh Scattering are introduced for linear molecules and experimental results are discussed with CO* as an example. The chapter ends with a warning that no reliable separation procedure has been developed for the orientational- and interaction-induced features. Neutron scattering with an emphasis on incoherent scattering is introduced in an admirably clear and efficient way. The scattering laws for translational and rotational diffusion are explained clearly and the importance of the elastic incoherent structure factor is stressed. As an example, the molecular motion in liquid furan is discussed: translational and rotational diffusion coefficients are obtained. A confrontation with the possibilities of NMR is sorely missed here. The basic NMR principles are condensed to a level precluding insight into the possibilities of this powerful technique. Only simple exponential decay is mentioned and T;’ is introduced as being proportional to the spectral density at the Larmor frequency. Explicit expressions later on in this chapter will therefore elude the beginner. Motional models are discussed adequately although a curious emphasis is put on a “model free” approach which by its very nature cannot be very informative on molecular motion. In the last chapter classical MD simulations are introduced and the simulation of dielectric, IR, Raman and light scattering is discussed. Reading this chapter may give students, among other things, a feeling for the molecular features in the correlation functions and for spectral densities obtained with spectroscopic techniques. To conclude, the editors and contributors certainly approximate their stated goal by collecting a wide range of information on different techiques in this book. Physical and Macromolecular Chemistry Leiden University Gorlaeus Laboratories Einsteinweg 55 2233 CC Leiden The Netherlands
J. C.
h3’TE