Atomic, Molecular, and Optical Physics (1986) / Chapter Skim
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7 Scientific Interfaces
7 Scientific Interfaces
Pages 126-150
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From page 126... ...
In this the boundaries disappear as the unity of science asserts its preeminence. Among the six interface areas that we have chosen to describe here astrophysics; materials research; surface science; and plasma, atmospheric, and nuclear physics instances of the underlying unity constantly occur.
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From page 127... ...
AMO physics ranges broadly in its applications to astronomy. The physical and chemical processes that created molecular hydrogen in the early pregalactic universe, which manufactured cyano-octatetrayne in interstellar clouds and propane in the atmosphere of Titan, which bring molecular clouds to the brink of gravitational collapse and trigger star formation, which control the abundance of ozone on the planet Earth, and which determine the radiative losses from stellar interiors, are all part of the body of AMO physics.
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From page 128... ...
Because the relevant atomic data are not available, a comprehensive description of the atomic processes occurring in a supernova remnant has yet to be achieved. Atomic Processes Many atomic processes play crucial roles in astrophysics.
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From page 129... ...
Radiation from interstellar molecules can extract energy from the interstellar clouds, cooling them to the brink of gravitational collapse. Two of the most fundamental astrophysical processes, nucleosynthesis and the chemical evolution of the galaxy, can be studied by observing the spatial distribution of isotopic molecules such as '3C~6O and ~2C~8O, though the task requires the mastery of the basic molecular chemistry.
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From page 130... ...
From its optical absorption spectrum the relative populations of the two lowest energy levels can be determined, and from this,
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From page 131... ...
Planetary atmospheres respond to solar ionizing and dissociating radiation in a complex array of atomic and molecular processes. The evolutionary paths followed by these atmospheres are affected by escape mechanisms driven by energy transfer in atomic and molecular collisions.
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From page 132... ...
The impact of AMO physics on surface science one of the liveliest areas in solid-state physics is so large that it is described separately in the next section. In this section, we describe three activities: light-scattering spectroscopy, metal clusters, and the creation of spin-polarized quantum fluids.
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From page 133... ...
Quasi-elastic light-scattering spectroscopy has been used to discover scaling phenomena in polymer solutions and to examine the moments of polymer cluster size distributions near the sol-gel transition. In polymer gels it has been used to discover a rich variety of hitherto unexpected first-order phase transitions.
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From page 134... ...
But by representing the exchange-correlation interaction with a simple local density-dependent exchange potential (ignoring correlation entirely) , and using a series of Gaussian functions to describe the atomic orbitals, the theory becomes tractable, even for disordered systems for which the standard band-structure methods are not applicable.
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From page 135... ...
The one continuous property known today for heavier clusters, from 2 to 15 atoms, is the photoionization potential. The earliest measurements of photoionization potentials were on alkali clusters; however, more recently photoionization thresholds as a function of cluster size have been reported for other species including rare-gas clusters, metal clusters, and a few molecular clusters such as (COW, (CS2)
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From page 136... ...
These systems are prime candidates for studying the interactions that broaden optical transitions and possibly for establishing secondary optical-frequency standards. The method has been applied to study the optical Bloch equations, the starting point for many theories in quantum optics.
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From page 137... ...
The techniques of spin-polarized hydrogen are being adapted to the production of polarized proton sources and targets for particle and nuclear physics. Other applications range from the creation of slow atomic hydrogen beams for superprecise spectroscopy and hydrogen scattering experiments to the production of polarized deuterons for the proposed use of polarized nuclei to obtain energy-producing fusion plasmas under less extreme conditions than previously contemplated.
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From page 138... ...
Other applications include electronic materials and processes, thin-film physics, corrosion, aircraft drag, and lubrication. Techniques from AMO physics such as laser spectroscopy and molecular-beam scattering are helping to revolutionize surface science.
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From page 139... ...
Recently, a series of experiments involving epitaxially grown thin films of xenon supported on silver have begun to reveal how the lattice dynamics of thin films evolve into those of a bulk crystal on a layer-by-layer basis. Metal Clusters Using lasers it is possible to vaporize a metal target within a supersonic nozzle, creating an intense ultracold beam of small clusters of the bare metal.
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From page 140... ...
FIGURE 7.1 Surface Scattering with a Supersonic Helium Beam. An atomic beam of helium constitutes a powerful probe for studying surfaces.
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From page 141... ...
Short intense laser pulses can reveal dynamical surface phenomena; coherent UV light can produce new types of nonlinear surface effects when it strikes adsorbed molecules. Laser light can trigger chemical changes on surfaces, in the substrate, and in the overlying gas.
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From page 142... ...
The Role of Atomic, Molecular, and Optical Data in Surface Science In addition to contributing experimental and theoretical techniques to surface science, AMO physics provides basic data that are essential
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From page 143... ...
Vibrational and rotational emission and absorption spectra for hot molecules are also needed. Stimulated desorption studies and sputtering spectroscopy require impact cross sections for ionization, branching ratios for dissociative ionization processes in small molecules, and spectroscopic data on ions and highly excited neutral species.
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From page 144... ...
Weakly ionized plasmas containing molecular gases raise a new set of questions concerning the influence of atomic and molecular processes on the evolution of the plasma. Molecular plasmas, energized by some external source, can by virtue of internal excitations modify the course and change the products of molecular reactions.
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From page 145... ...
This is also true for the atomic and molecular processes that follow auroral bombardment at high altitudes. Light from the aurora is a potentially powerful diagnostic probe of the exciting source and of the acceleration mechanism that appears to occur.
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From page 146... ...
This has been an indispensable tool of nuclear physics for decades but now contributes more information than ever. The second is the use of atomic techniques to provide polarized nuclei for sources and targets in nuclear experiments.
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From page 147... ...
These electromagnetic properties of the nucleus can be parameterized in terms of electric and magnetic moments that describe the size, shape, and charge and current distributions of the nuclear constituents. The spins, the magnetic dipole moments, and the electric quadrupole moments of a wide variety of nuclei can be found from measurements of the hyperfine interaction made by two atomic techniques: high-resolution optical spectroscopy and atomic-beam magnetic resonance.
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From page 148... ...
The earliest evidence that atomic nuclei possess spin and magnetic moments came from atomic physics, and as new experimental techniques have been developed, the range and precision of these nuclear studies have increased steadily. The drawing illustrates a number of atomic experiments on nuclear properties being carried out at ISOLDE, the on-line isotope separator at CERN (Geneva)
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From page 149... ...
The remarkable recent progress made by atomic physicists in trapping ions and atoms for long periods of time is certain to be exploited for further high-precision measurements of nuclear moments. Polarized Nuclear Sources Nuclear physics relies on techniques from atomic physics for producing the spin-polarized projectiles and target atoms that are being used increasingly in nuclear-reaction experiments.
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From page 150... ...
can now be determined by crystal blocking techniques that exemplify the overlap of nuclear physics with both condensed-matter and atomic physics. Finally, we note here a new development: an experiment that is being carried forward at a laboratory of particle physics but that represents a confluence of particle, nuclear, and atomic physics.
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