| RefNo | EC/1995/42 |
| Level | Item |
| Title | Fano, Ugo: certificate of election to the Royal Society |
| Date | 1988 |
| Description | Certificate of Candidate for Election to Foreign Membership. Citation typed. Citation continued on separate piece of paper pasted onto certificate |
| Citation | Ugo Fano has been a major intellectual force in theoretical atomic, molecular and optical physics, and has shown remarkable originality and ingenuity sustained over several decades. His research school at the University of Chicago has been a principal source of young theorists in atomic physics. He is famous for many innovative ideas. It is characteristic of his studies to introduce unifying concepts and procedures which reduce apparently diverse and complex phenomena to a simple and practical description.
The interactions between a continuum energy spectrum and the discrete energy levels of the bound states that may be embedded in it is a fundamental phenomenon of physics, demonstrated in its most elegant form by precision experiments on electron and photon excitation of atomic and molecular systems. The theory was worked out in classic papers by Ugo Fano, who developed a simple analytical representation of the effects of the interaction. The profiles of the resonance structures that occur are called Fano profiles. The Fano formula is of remarkable simplicity, and it reproduces a broad range of experimental measurements in atomic and molecular spectroscopy and in collisional spectroscopy.
Ugo Fano's work on resonance structures was also extended, in collaboration with Cooper and Prats, to identify new quantum numbers, + and -, which classified the doubly excited states of helium. More recently, he has been developing new ways of looking at two-electron correlation effects in atoms based mathematically on the use of hyperspherical coordinates and exhibiting again considerable physical insight. This work has lead to the deep understanding which now exists of the properties and classification of doubly excited states and two-electron correlations in atoms and molecules.
Another area where Fano has made outstanding contributions has been his work with Cooper on the general characteristics of the optical oscillator strengths of atoms. This led to Fano's fundamental prediction that photoelectrons ejected by unpolarised light from heavy atoms in the neighbourhood of certain minima in the cross sections would be strongly polarised by the spin-orbit interaction. This prediction, which has been verified by many experiments, is now referred to as the Fano effect, and marked the start of many recent developments in the theory and application of polarised electrons.
Slow heavy particle collisions are commonly interpreted in the framework of the adiabatic Born-Oppenheimer molecular representation, in which potential energy curves of molecular states of the same symmetry cannot cross. A body of data was obtained experimentally that appeared to demand an interpretation involving many molecular states interacting in a complicated way. Fano, working with Lichten, introduced the idea of diabatic molecular states into collision theory. Diabatic potential energy curves of the same molecular symmetry do cross. The data could be plausibly interpreted as due to a collision taking place along a single diabatic potential energy curve. A similar concept can be used to understand the spectrum of molecular X-rays produced in more energetic collisions. The idea of diabatic states has been rigorously formulated and is now widely used in atomic collision theory and in studies of molecular photodissociation.
During the last twenty years, M.J. Seaton has developed muiltichannel quantum defect theory into a tool of enormous power in the interpretation and predictionof [sic] the energy level structure of highly excited atomic and ionic systems. Fano showed great technical skill and deep physical insight in generalizing the theory to molecular Rydberg states which not only undergo pre-ionization, as autoionization in atoms, but also predissociation. Again a simple mathematical theory, this extension of an existing theory permitted a systematic explanation of a great wealth of previously confusing data. The theory also has great predictive power.
Fano is also a master of angular momentum theory, and his book with Giulio Racha is a highly original, fundamental contribution which clarifies the underlying mathematical structure. He developed this theory to describe the interaction between atomic configurations containing several open shells which has been central to most subsequent atomic structure and electron-atom scattering calculations. He has used the theory with extraordinary ingenity [sic] in the analyses of coherence, polarization, alignment and angular distributions in experiments involving particle and photon collisions. He used it also to develop with E.S. Chang the frame transformation method for electron-molecule scattering, in which the transformation from an adiabatic description valid at small distances to the physically appropriate asymptotic form at large distances is elegantly accomplished.
In his early career Ugo Fano made pioneering contributions to the theory of the absorption of energetic particles and X-rays in matter. This was of considerable importance in radiological physics and dosimetry and included a study of the statistical fluctuations of the ionisation yield, the magnitude of these fluctuations now being called the Fano factor. |
| AccessStatus | Closed |
Fellows associated with this archive
| Code | PersonName | Dates |
| NA964 | Fano; Ugo (1912 - 2001) | 1912 - 2001 |