The Laboratory, 1991-2000

In July 1986 one of the first of the committees appointed to make periodic reviews of departments for the Faculty Boards reported on 'The Future of Chemistry'. Among its recommendations was, first, that a new building was desperately needed to relieve the overcrowding and unsatisfactory conditions in many laboratories and, secondly, that the Departments of Theoretical and Physical Chemistry should be amalgamated. Little could be done about the first recommendation since there was then no source from which the bulk of the cost could be raised. Overcrowding was a problem that affected all three laboratories but was least severe in the P.C.L.. Norman March, the Coulson Professor of Theoretical Chemistry, was not happy with the second recommendation since he held to Coulson's original vision that his subject was the theory of all chemistry and not solely that of physical chemistry. The only immediate outcome was that Colin Ryde, the new Administrator in the P.C.L., became also the Administrator of Theoretical Chemistry. With Norman March's retirement in 1994 the amalgamation finally took place.

A second Faculty Board Committee then recommended the amalgamation of all three departments into a unified Department of Chemistry, and again repeated the urgency for a new building. The new Department came into being in 1997 with Graham Richards of the P.T.C.L. as the first Chairman, and this was undoubtedly a necessary step before bids could be made for the estimated £60 000 000 needed for a building on the opposite side of South Parks Road from the existing laboratories. The securing of £30 000 000 from the new Joint Infrastructure Fund established by the Research Councils and the Wellcome Trust, and the raising of a similar amount of money from a variety of other sources, enabled a start to be made in December 2000. The existing Sub-Departments, as they have now become, have retained a great deal of their day-to-day independence and distinctive character, and this account is restricted to what is now the Physical and Theoretical Chemistry Laboratory. Here the amalgamation with Theoretical Chemistry has gone smoothly and the extra space required in the P.C.L. was found when some of existing experimental research moved from 1993 onwards into the New Chemistry Laboratory (the old Pharmacology Laboratory, renovated by the University). These groups retain, however, their academic and administrative links with the P.T.C.L.

Research in physical chemistry arose out of the study of ionic and non-ionic liquid solutions towards the end of the of the 19th century. It expanded into such fields as chemical kinetics, in both liquids and gases, by using classical methods such as measuring changes of gas pressures (a speciality of Hinshelwood), but it was only with the advent of quantum mechanics that the much more detailed information at the single molecule level could be revealed by spectroscopic and similar methods. Initially this information was restricted to the gas phase and this new branch of the subject often came to be called chemical physics. The distinctions are now blurred but the work of the Laboratory can still be broadly divided into the study of the details of molecules acting one or two at a time, usually in the gas, and the study of the collective properties of groups of molecules or of matter in bulk in solids and liquids and at interfaces. For many years the numbers in the Department in each section of the field have been comparable and this has remained true throughout the last decade. Of the 22 members of the staff who are now contributing to the research programme, 10 can be identified broadly with the first group and 11 with the second, although there are some who have crossed boundaries or whose work is not so easily categorised.

Let us start with the first group since this was strengthened by the appointment of John Simons to the Dr Lee's chair in 1993, bringing with him from Nottingham, Mark Brouard who was appointed to the Lectureship that had been vacant since Mike Pilling had left for Leeds in 1989. They joined a laboratory in which there were several well-established spectroscopic groups.

John Brown studies small, open-shell molecules at a variety of wavelengths. In the far-infrared region he has developed a new microwave discharge source that has allowed him to produce many new species in detectable concentrations, including such ions as H₂O⁺ and NH⁺. Low frequency bending vibrations have been detected in CCN, HCCN, and FeD₂. In the infrared region he has detected, for the first time, the radical FeH₂, through the observation of transitions involving its anti-symmetric stretching vibration. In the visible and near-ultraviolet regions he has analysed the spectra of such novel species as InOH and In₂O, and has continued his analysis of the complicated visible spectrum of FeH, a molecule of great astronomical interest.

At even shorter wave-lengths Tim Softley has developed coherent extreme ultraviolet sources and has applied them to study the ZEKE (zero-kinetic-energy) photoelectron spectra of small molecules and the lifetimes of Rydberg states in electric fields. By using pulsed-field ionization of Rydberg states he can select rotation-vibration states of molecular ions and use them to study quantum state effects in bimolecular ion-neutral molecule reactions that are relevant to upper atmosphere and interstellar chemistry. He has also developed a new technique for studying the photodissociation of molecules near their thresshold energies.

The basic theory of Rydberg states of polyatomic molecules was developed by Mark Child and Christian Jungen of Orsay in 1991. They have since analysed in detail many such spectra, including those for the water molecule, and have suggested a proper interpretation of ZEKE intensities. Mark Child's other main interest has been to use the techniques of non-linear classical dynamics to interpret the quantal distributions of highly excited vibrational states; this work arose out of his earlier work on local mode vibrations. A new specialised interest is 'quantum monodromy' which is an analysis of the states around a cylindrically symmetrical barrier such as those around the barrier to linearity in the molecule H₂O.

Photoelectron spectroscopy of ions is John Eland's field and his many ingenious experiments have been named by increasingly bizarre acronyms. The method of photoelectron photoion-photoion coincidence (PEPIPIPCO) was developed ten years ago and has now been applied to many molecules; it has led to a theoretical model of di-cation breakdown. A new form of the technique, with position-sensitive detection of products, gives full kinematic information on three-body dissociations and allows concerted and sequential reactions to be distinguished directly. The technique of threshold photoelectron coincidence (TPEsCO), developed with colleagues in France, gave the first vibrationally-resolved di-cation decay rates. The most recent addition to the armoury, velocity imaging photoion coincidence (VIPCO) allows the photoelectron angular distribution to be measured as if from molecules fixed in space; it has led to the observation of a new reaction, ion-triple formation.

Van der Waals molecules are weakly bound groups of two or more molecules held together by intermolecular forces. Brian Howard has contributed greatly to our understanding the nature of these forces and the potential surfaces on which the constituent atoms move. In the early 1990s he concentrated on the infrared spectroscopy of complexes containing tetrahedral molecules. The spectra showed considerable internal motion associated with the hindered rotation of molecules such as methane and silane. These were used to determine accurate anisotropic potential surfaces for complexes of a rare gas atom with a XH₄ molecule. The forces are mainly dispersion and electrostatic but he has found small valence contributions to the potential in complexes in which the delocalisation of an unpaired electron can be studied, such as NO + HF. Of particular interest is the weakly bonded complex of SO₃ and H₂O, which is distinct from the valence-bonded molecule H₂SO₄. His most recent work has been on the interaction of simple chiral molecules which he hopes can be used as models for chiral interactions in biological systems.

The dynamic aspects of molecular collisions in the gas were the centre of Stephen Simpson's work during most of his 28 years in the laboratory, in particular the measurement of the rate of transfer of vibrational energy into and out of molecules. Most recently he has extended this study to energy exchange in molecules adsorbed on solid surfaces. He retired in 1997 and the work stopped in this laboratory but, with characteristic enthusiasm, he is continuing it abroad in collaboration with American colleagues.

The advent first of spectroscopy, then of lasers and molecular beams has transformed the study of chemical reactions in the gas phase. Gus Hancock has used these techniques to measure the quantum yields of the formation of the oxygen atom in the ¹D state from the photolysis of ozone. The result has had a profound effect on the calculated oxidising capacity of the troposphere, because the reaction of O(¹D) with water vapour initiates the formation of the OH radical, 'Nature's atmospheric detergent'. (This research has been recognised by the award of the 2000 Italgas Prize.) He is now heavily involved in the use of compact diode lasers for measurements of high sensitivity in reaction dynamics and atmospheric science.

The theory of chemical reaction dynamics has been the principal field of David Manolopoulos since his move to Oxford in 1995. He has developed a computer program for studying quantal effects in elementary atom + diatom reactions such as Cl + HD and F + HD. Here the weak van der Waals forces in the entrance valley have a decisive effect on the outcome of the reaction when the HD is rotationally unexcited. He has also collaborated with Mark Child in studying the quantal phenomenon of 'geometric phase', where they have generalised a result previously known for a simple two-fold electronic degeneracy to a n-fold degeneracy, thus explaining some puzzling results of a microwave cavity experiment.

Richard Wayne published the second edition of his Chemistry of Atmospheres in 1991 and the third edition in 2000. His research has included extensive studies of the reactions of NO3 with peroxy species, which are important in the night-time chemistry of the troposphere, and with biogenic species in the atmosphere. A second interest has been the reactions of the chlorine atom with anthropogenic and biogenic species in the troposphere. His work extends also to the stratosphere, where he seeks so far unknown catalysts and catalytic cycles (with detailed studies of CF₃O and CF₃O₂, and I and IO-based cycles) and is investigating the chemistry of 'new' reservoir compounds such as the higher oxides of chlorine, ClO₃, Cl₂O₃, etc.

John Simons and Mark Brouard work together in some of their studies of reaction dynamics. They have developed and exploited new, laser-based Doppler techniques for determining the linear and angular momentum distributions among the state-resolved products of reactive collisions. These have provided, for the first time a direct entry into the shapes and anisotropies of the reactive potential energy surfaces that control the dynamics, and lead to direct tests of theory. Brouard's work has extended to the determination of rotational angular momentum polarisation effects in elementary photochemical and bimolecular reactions. He has recently measured the rotational angular momentum orientation of the OH products of the H + O₂ reaction, an effect that has probably not been observed before in a bimolecular reaction. Simons's more recent work has extended to the spectroscopy of small biomolecules. He uses IR and UV lasers, mass spectroscopy, and ab initio compution to characterise the conformational landscapes and supramolecular structures of small, pharmacologically important molecules, biomolecular building blocks, and their hydrated clusters. Highlights of this work include the first complete conformational analysis of some amino acids and neurotransmitters, and the structural assignment of hydrated clusters of model peptide conformers.

Discussion of such biological work leads naturally to the work of Graham Richards in condensed phases, and so to the other main branch of the Laboratory's research. His theoretical group has been concerned with a wide range of problems in molecular biophysics, often popularly described as 'drug design'. The increase in the power of computers allowed the study of DNA, proteins, and biological membranes, with the calculation of free energies rather than the less informative enthalpies. The topic of 'molecular similarity', largely created by his group, and the introduction of pattern recognition techniques have become the subjects of international meetings.

In 1989 his group gave birth to the company Oxford Molecular which was floated on the London Stock Exchange in 1994, only to be sold to American companies in 2000. In the same year the group received $750 000 from the National Foundation for Cancer Research to set up a Centre for Computational Drug Discovery.

Richard Compton's group is the most productive in the Laboratory, as measured by the number of papers published each year. He works in collaboration with Barry Coles and their work has three main strands. The first is sonochemistry - the combination of exposure to ultrasound with other chemical techniques, in his case electrochemical. This is used in electrosynthesis and in difficult analytical problems such as stripping voltammetries in wine, beer, blood, and petrol. The second strand is the computer simulation of electrode reactions. This is used to predict flow patterns around electrodes and to track concentrations of species as they change in space and time. Their simulation programs are now available on the Web for all to use freely. The third group of projects includes novel electrode materials, such as boron-doped diamond, and a variety of techniques of combining electrochemistry with other 'perturbations', as in photoelectrochemistry, sonophotoelectrochemistry, laser-activated voltammetry, and microwave-enhanced electroanalysis.

John Foord's work involves a different kind of solid surface, one in which the metal or other solid is exposed to and manipulated in a high vacuum. Such research has a pivotal role in the development of advanced materials and in controlling their functionality. Work on the epitaxial growth of compound semiconductors has identified many of the microscopic surface chemical steps that control macroscopic growth. This establishes important principles in chemical vapour deposition. The first reported molecular beam growth of films of diamond has led to the determination of the key steps in diamond formation. The chemical manipulation of the surface electronic properties of this material has enabled new applications to be found.

With Bob Thomas's work we move, in the main, from the solid surface to the liquid. In the early nineties his main effort was to develop the neutron reflection technique. He showed that by selective deuteration of fragments of sections of surfactant molecules it was possible to enhance the resolution with which neutron reflection could be used to determine the structure of surfactant films at interfaces. More recently he has looked at more complex systems with mixtures of surfactants or of a surfactant with a polymer, again using the method of deuterium labelling to pick out the features of interest. The structure and behaviour of these systems were not at all understood but, by choosing appropiate model systems, he is working his way towards sensible working models of them.

Where Thomas has been concerned with structure, Colin Bain is interested primarily in the dynamics of surface films, originally by the method of optical sum-frequency spectroscopy for studying molecules at dielelectric interfaces. He has now added other techniques such as ellipsometry, Raman scattering, FTIR, and laser Doppler scattering, and he uses the international facilities at the ISIS laboratory and the FELIX laser in The Netherlands. In these ways he has been able to identify and characterise phase transitions in monolayers of surfactants at air-water and oil-water interfaces. He has obtained spectra in lubricant films at pressures up to 5 kbar and can study the adsorption kinetics and Marangoni flow at liquid interfaces on time scales down to 1 ms.

Keith McLauchlan uses flash photolysis ESR and electron spin polarisation to study the recombination of radical pairs in liquid solutions. In 1992 this work led him to suggest what is still the only accepted mechanism by which magnetic fields might affect chemical reactions of biological interest, and so maybe to throw some light on the much-discussed possibility that overhead power lines might be a hazard. He, Peter Hore, and Christiane Timmel have since studied this effect in detail and have shown that in almost cases the probability of radical recombination is changed in all fields down to zero strength if the diffusional motion of the radicals is restricted. A related phenomenon, found in 1997 and as yet observed only in their laboratory, is an effect of radiofrequency fields, resonant with the hyperfine frequencies of the radicals, on the rates of recombination. A novel apparatus has now been built to study this further. Peter Hore's other work has been the development of a new stopped-flow technique for following protein folding in real time and for probing the structures of partially folded proteins at the level of the individual amino-acid residues. This work uses the method laser-induced photo-CIDNP, or Chemically Induced Dynamic Nuclear Polarization, and is carried out in collaboration with a group in the Oxford Centre for Molecular Sciences. Solid-state NMR was the field of research of Stephen Wimperis, a Royal Society University Fellow in the Laboratory until his departure for a Readership at Exeter University in 1999.

The theory of the solid state is the field of David Logan and Paul Madden. Logan studies the electronic structure of solids, including both pure disordered and pure interacting electron systems, and the subtle interplay between the two. His most recent work has centered on a new many-bodied approach to strongly correlated electrons, the Local Moment Approach, or LMA. The focus here is on physical models applicable to a wide range of correlated electron materials, in particular quantum impurity models and their effective lattice-based counterparts such as the Hubbard and periodic Anderson models. The aim of the LMA is to get a theoretical handle on the notoriously difficult problem of dynamics, such as the single-particle spectra probed by photoelectron spectroscopy. Madden aims to develop realistic representations of the interatomic interactions in computer simulations of metallic and ionic solids. Originally he followed the ideas developed by Car and Parinello and used ab initio descriptions of the electronic state, but more recently has developed new schemes in which approximate representations of the electronic structure appropriate to each class of materials were used. These are far more computationally efficient than an ab initio description and have allowed hin to make large-scale, ground-breaking simulations of metals, ionic solids and liquids, and colloids. Perhaps the most significant aspect of this work has been the identification and quantitative description of the interactions possible for covalent behaviour in ionic systems.

The works of Peter Atkins probably have more readers than those of all the rest of the Laboratory put together. The last decade has seen the publication of the 5th and 6th editions of his textbook Physical Chemistry, the 1st and 2nd of Elements of Physical Chemistry, the 2nd and 3rd of Inorganic Chemistry, and the 3rd of Molecular Quantum Mechanics. Other books have ranged outside the confines of these successful textbooks. The duties of the Teaching Laboratory Officer do not formally require research but Hugh Cartwright has written Applications of Artificial Intelligence to Chemistry which is the first book in its field and is having a real influence.

Computing is an essential adjunct to all research, and nowadays also to the workshops, administration, and finance of the Laboratory. During the 1990s the Sun server was upgraded several times under the supervision of Pete Biggs who was appointed IT Manager in 1994. At the same time more amd more groups acquired their own servers, and the University Service (OUCS) no longer provided computing power in the form of central main-frames. In 1997 the theoreticians in the Laboratory got an EPSRC grant for a multi-processor machine and, since the Sun server was becoming obsolete, the two requirements were combined and a large Silicon Graphics Origin 2000 machine was bought. For a short time, the Laboratory had the most powerful machine in the University.

Part II: A Personal View Appendix