He always stressed to his students that they begin attacking a problem by developing a completely general theoretical analysis before making approximations and simplifications applicable to particular situations. Chris Greene of Purdue University another former student of Fano does, however, remember as a graduate student asking Fano in the late s a question about his famous paper that revised and extended the theoretical explanation of the asymmetric peaks that appear in atomic excitation spectra. At that time, Fano seemed surprised people were still interested in that paper.
Rau recalls a similar interaction. Fano told him that the formalism was obsolete and could be done much better, as in their book Atomic Collisions and Spectra 5. The book, Rau explained, coupled the work with another of Fano's favourite themes; he liked to see spectroscopy bound states and collisions and scattering continuum states on an equal footing, belonging to the spectrum of the same Hamiltonian. While Greene does note the power of the later quantum defect theory, he mentioned that the earlier Fano lineshape theory was arguably more broadly applicable, for example, to photonic systems and condensed-matter systems where quantum defect ideas are less obviously useful.
How did Fano come to work on spectra and their lineshapes? Starace explained that Fano was accepted into Enrico Fermi's group and was also taken under the wing of a young faculty member, Emilio Segre.
Although he published the result in 6 , Greene and Starace confirmed that some years later, Fano was browsing Fermi's notebooks and found that Fermi himself had solved the problem within days of presenting it to Fano. An account of the details, particularly well worth reading for any advisor of students, reveals the selfless and nurturing mentoring bestowed by Fermi 4.
Fermi may have solved the problem later the same day he gave it to Fano, but he refused co-authorship 4. It is important to note that Fano's contributions go well beyond these 'lineshape' works.
With regard to his other important findings, both Starace and Greene mentioned the research on the description of states in quantum mechanics by density matrix and operator techniques 7. Starace noted the particularly clear and physical presentation of the techniques applied to a variety of complex physical phenomena in that work and also paid tribute to another manuscript on spectral distribution of atomic oscillator strengths 8 , which set the stage for theoretical understanding of the new synchrotron atomic spectra in the vacuum-ultraviolet energy region.
While much has been written about Fano's achievements, less has been discussed about what kind of person he was to work with. Having arrived as a graduate student at the University of Chicago in , Starace found Fano was personally very warm, demanding of his students and did not tolerate carelessness or foolishness. He was very interactive, joining the group for lunch at least three times a week, with discussions not limited to physics, but extending to politics and the arts.
It was at these lunch meetings that Starace and the group saw another side of Fano, the passionate intellectual. Fano, U. Real spectra may differ considerably from these synthesized ones in that lines shown here are not seen there or that lines occur which are not included in the above pictures. See the lightning spectrum as an example. The relative intensities of the lines depend on the circumstances of excitation and de-excitation of the atoms and ions and emission and possible re-absorption of the photons.
Assuming a thin plasma sheet in thermodynamic equilibrium, only temperature and electron density are important. But not so in most other cases.
The spectra which, after the one of hydrogen, are the simplest to explain, are those of the alkali metals. Stine, R. ST Phys. Quasiclassical predictions of final vibrational state distributions in reactive and nonreactive collisions. Currents of energetic charged particles are flowing at high altitude along the magnetic field lines the single particles following coiled paths. Deepika Janakiraman, K. Whiteley, Anthony J.
An electric spark in air produced with a small Wimshurst machine, photographed through a diffraction grating. There is a continuous background due to photon emission by unbound electrons when captured by ions. The violet lines are blue in the picture, and the yellow and orange lines of nitrogen show up green and red instead. Spectral colours cannot be reproduced faithfully in photography. This has been discussed already in connection with experiments with the prism.
Click on the above spectrum to see an image which has been processed to make it somewhat more similar to the visual impression! The four 2p-electrons may be distributed over six possible single-particle states.
If there were no interaction between the electrons, all the fifteen possibilities would lead to the same energy. But due to their charge, the electrons repel each other. Elektrons with parallel spins tend to avoid each other due to the Paiuli principle.
Thus, parallel spins are energetically favoured. The larger the total orbital angular momentum, the less is the mutual overlap of the electron densities. For the lighter elements, spin-orbit interaction is only small. As long as there is no preferred direction in space, total angular momentum is conserved and the states can be labelled by its quantum numbers. Usually total angular momentum is denoted by capital letters S, P, D, F. Thus the lowest few levels of oxygen are the following experimental data taken from the compilation of Sansonetti und Martin :.
But why are these lines not seen under laboratory conditions?
In the treatment of dyes emission and absorption probabilities are dealt with in some nore detail. As mentioned in the beginning, light emission from single atoms can be observed only seldom in nature. Lightnings and polar lights are the only prominent earthly examples, but if seen, they are impressive! Currents of energetic charged particles are flowing at high altitude along the magnetic field lines the single particles following coiled paths. They come closest to the ground at high latidudes. In collisions, energy is transferred to the particles of the upper atmosphere and is then radiated off as visible light.
The polar light originates from heights between roughly and km; in times of strong solar activity also much higher, then it can be seen even at middle latitudes. The composition of the atmosphere at these heights is very different from that of the lower layers: nitrogen molecules and oxygen atoms are much more abundant than all the rest. It is not seen at larger heights since the 1 S-state is not reached from the 3 P ground state in collisions with electrons or protons.
It is assumed that this state is produced in collisions of O 3 P with excited nitrogen molecules which give off their energy and take over angular momentum:. It has already been mentioned that under normal terrestrial conditions only the noble gases consist of single atoms. All other elements have the tendency that their atoms bind to other ones, forming molecules, the energy of which is lower than that of the separate constituents.
In general, the charge distribution in a compound molecule of different atoms is not symmetric, an electric dipole moment results, the molecules attract each other and thus condense to a liquid or a solid. Small molecules built from the lighter elements are colourless. As the free atoms, they cannot absorb visible light; only in the ultraviolet region the photons have sufficient energy to electronically excite the molecule. On the other hand, the vibrational excitations of the molecules lead to absorption and emission of infrared radiation and causes only very faint colour, as in water.
Computed visible part of the hydrogen spectrum. The scale gives the wavelength in nm nanometers. In experiment, the spectral lines are images of the spectroscope's entrance slit which occur on different places depending on the wavelength. Scale: wavelength in nm. Only the stronger lines are shown.
Data source as above. Northern light, February 22, , UT, Finland close to the polar circle. The animation of this and the next picture does not work if the Adobe Flash Player is deactivated or not installed. Between and km molecular nitrogen and atomic oxygen are the most abundant. Typical spectrum of greenish polar light. By removing or setting checkmarks the different components can be identified. The units of the left scale are kR kiloRayleigh.
Atomic Collisions and Spectra provides an overview of the state of knowledge on atomic collision physics. The book grew out of lecture notes for a succession of. Buy Atomic Collisions and Spectra on giuliettasprint.konfer.eu ✓ FREE SHIPPING on qualified orders.
These units do not measure perceptual lightness, but the number of photons per unit area and time. The state with lowest energy is spherically symmetric without any nodes. For the next higher possible energy, two states of different shape are possible. Progress report, June 1, May 31, Title: Observation of luminescent spectra in low energy ion-neutral collisions. Full Record Other Related Research. Abstract The experiments reported provide detailed information on the fundamental nature of energy transfer processes in ion-molecule or atom-molecule collisions.
Authors: Leventhal, J. Publication Date: Research Org.