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The collision of electrons with molecules and molecular ions is a
fundamental pro cess in atomic and molecular physics and in
chemistry. At high incident electron en ergies, electron-molecule
collisions are used to deduce molecular geometries, oscillator
strengths for optically allowed transitions, and in the case of
electron-impact ionization, to probe the momentum distribution of
the molecule itself. When the incident electron energy is
comparable to or below those of the molecular valence electrons,
the physics involved is particularly rich. Correlation and exchange
effects necessary to describe such collision processes bear a close
resemblance to similar efft: cts in the theory of electronic
structure in molecules. Compound state formations, in the form of
resonances and vir tual states, manifest themselves in experimental
observables which provide details of the electron-molecule
interactions. Ro-vibrational excitations by low-energy electron
collisions exemplify energy transfer between the electronic and
nuclear motion. The role of nonadiabatic interaction is raised
here. When the final vibrational state is in the continuum,
molecular dissociation occurs. Dissociative recombination and
dissociative attachment are examples of such fragmentation
processes. In addition to its fundamental nature, the study of
electron-molecule collisions is also motivated by its relation to
other fields of study and by its technological appli cations. The
study of planetary atmospheres and the interstellar medium
necessarily involve collision processes of electrons with molecules
and molecular ions."
The NATO-Advanced Study Institute on "Collision Theory for Atoms
and Molecules" was made possible by the main sponsorship and the
generous financial support of the NATO Scientific Affairs Division
in Brussels. Belgium. Special thanks are therefore due to the late
Dr. Mario Di Lullo and to Dr. Craig Sinclair. of this Division. who
repeatedly advised us and kept us aware of administrative
requirements. The Institute was also assisted by the financial aid
from the Scientific Committees for Chemistry and Physics of the
Italian National Research Council (CNR). The search and selection
of a suitable location. one which participants would easily reach
from any of Italy's main airports, was ably aided by the Personnel
of the Scuola Normale Superiore of Pisa and made possible by its
Directorship. Our thanks therefore go to its present director.
Prof. L. Radicati. and to its past director. Prof. E. Vesentini who
first agreed to our use of their main building in Pisa and of their
palatial facilities at the "Palazzone" in Cortona.
Until recently, the field of atomic and molecular collisions was
left to a handful of practitioners who essentially explored it as a
branch of atomic physics and gathered their experimental re sults
mainly from spectroscopy measurements in bulk. But in the past ten
years or so, all of this has dramatically changed, and we are now
witnessing the rapid growth of a large body of research that
encompasses the simplest atoms as well as the largest mole cules,
that looks at a wide variety of phenomena well outside purely
spectroscopic observation, and that finds applications in an
unexpectedly broad range of physico-chemical and physical pro
cesses. The latter are in turn surprisingly close to very important
sectors of applied research, such as the modeling of molecular
lasers, the study of isotope separation techniques, and the energy
losses in confined plasmas, to mention just a few of them. As a
consequence of this healthy state of affairs, greatly diversified
research pathways have developed; however, their specialized
problems are increasingly at risk of being viewed in isolation,
although they are part of a major and extended branch of physics or
chemistry. This is particularly true when it comes to the theory of
this work -- where well-established methods and models of one
subfield are practically unknown to researchers in other subfields
-- and, consequently, the danger of wasteful duplication arising is
quite real."
This volume is the outgrowth of a workshop held in October, 2000 at
the Institute for Theoretical Atomic and Molecular Physics at the
Harvard- Smithsonian Center for Astrophysics in Cambridge, MA. The
aim of this book (similar in theme to the workshop) is to present
an overview of new directions in antimatter physics and chemistry
research. The emphasis is on positron and positronium interactions
both with themselves and with ordinary matter. The timeliness of
this subject comes from several considerations. New concepts for
intense positron sources and the development of positron
accumulators and trap-based positron beams provide qualitatively
new experimental capabilities. On the theoretical side, the ability
to model complex systems and complex processes has increased
dramatically in recent years, due in part to progress in
computational physics. There are presently an intriguing variety of
phenomena that await theoretical explanation. It is virtually
assured that the new experimental capabilities in this area will
lead to a rapid expansion of this list. This book is organized into
four sections: The first section discusses potential new
experimental capabilities and the uses and the progress that might
be made with them. The second section discusses topics involving
antihydrogen and many-body phenomena, including Bose condensation
of positronium atoms and positron interactions with materials. The
final two sections treat a range of topics involving positron and
positronium interactions with atoms and molecules.
The collision of electrons with molecules and molecular ions is a
fundamental pro cess in atomic and molecular physics and in
chemistry. At high incident electron en ergies, electron-molecule
collisions are used to deduce molecular geometries, oscillator
strengths for optically allowed transitions, and in the case of
electron-impact ionization, to probe the momentum distribution of
the molecule itself. When the incident electron energy is
comparable to or below those of the molecular valence electrons,
the physics involved is particularly rich. Correlation and exchange
effects necessary to describe such collision processes bear a close
resemblance to similar efft: cts in the theory of electronic
structure in molecules. Compound state formations, in the form of
resonances and vir tual states, manifest themselves in experimental
observables which provide details of the electron-molecule
interactions. Ro-vibrational excitations by low-energy electron
collisions exemplify energy transfer between the electronic and
nuclear motion. The role of nonadiabatic interaction is raised
here. When the final vibrational state is in the continuum,
molecular dissociation occurs. Dissociative recombination and
dissociative attachment are examples of such fragmentation
processes. In addition to its fundamental nature, the study of
electron-molecule collisions is also motivated by its relation to
other fields of study and by its technological appli cations. The
study of planetary atmospheres and the interstellar medium
necessarily involve collision processes of electrons with molecules
and molecular ions."
Until recently, the field of atomic and molecular collisions was
left to a handful of practitioners who essentially explored it as a
branch of atomic physics and gathered their experimental re sults
mainly from spectroscopy measurements in bulk. But in the past ten
years or so, all of this has dramatically changed, and we are now
witnessing the rapid growth of a large body of research that
encompasses the simplest atoms as well as the largest mole cules,
that looks at a wide variety of phenomena well outside purely
spectroscopic observation, and that finds applications in an
unexpectedly broad range of physico-chemical and physical pro
cesses. The latter are in turn surprisingly close to very important
sectors of applied research, such as the modeling of molecular
lasers, the study of isotope separation techniques, and the energy
losses in confined plasmas, to mention just a few of them. As a
consequence of this healthy state of affairs, greatly diversified
research pathways have developed; however, their specialized
problems are increasingly at risk of being viewed in isolation,
although they are part of a major and extended branch of physics or
chemistry. This is particularly true when it comes to the theory of
this work -- where well-established methods and models of one
subfield are practically unknown to researchers in other subfields
-- and, consequently, the danger of wasteful duplication arising is
quite real."
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