29 research outputs found
Highly Excited States of Small Molecules and Negative Atomic Ions
Excited states of atoms and molecules exhibit a rich array of diverse phenomena. This dissertation examines two exotic states of atoms at such excited levels: Rydberg molecules and atomic negative ions. Rydberg molecules are formed by a Rydberg atom and one or more ground state atoms, and can be highly polar due to their unusual electronic wave functions and enormous bond lengths. This dissertation expands the theory of these molecules by studying the formation and structure of polyatomic molecules, multichannel Rydberg molecules formed from divalent atoms, and spin effects and relativistic interactions. It also details intermolecular forces between Rydberg molecules, their manipulation via external fields, and their dependence on the intricacies of electron-atom scattering. This electron-atom interaction is also the main component of the latter portion of this thesis, which studies doubly excited states of alkali negative ions in very polarizable and nearly degenerate atomic states. Photodetachment of these states reveals electron correlation and long-range forces stemming from their high excitation
Trilobites, butterflies, and other exotic specimens of long-range Rydberg molecules
This Ph.D. tutorial discusses ultra-long-range Rydberg molecules, the exotic
bound states of a Rydberg atom and one or more ground state atoms immersed in
the Rydberg electron's wave function. This novel chemical bond is distinct from
an ionic or covalent bond, and is accomplished by a very different mechanism:
the Rydberg electron, elastically scattering off of the ground state atoms,
exerts a weak attractive force sufficient to form the molecule in long-range
oscillatory potential wells. In the last decade this topic has burgeoned into a
vibrant and mature subfield of atomic and molecular physics following the
rapidly developing capability of experiment to observe and manipulate these
molecules. This tutorial focuses on three areas where this experimental
progress has demanded more sophisticated theoretical descriptions: the
structure of polyatomic molecules, the influence of electronic and nuclear
spin, and the behavior of these molecules in external fields. The main results
are a collection of potential energy curves and electronic wave functions which
together describe the physics of Rydberg molecules. Additionally, to facilitate
future progress in this field, this tutorial provides a general overview of the
current state of experiment and theory.Comment: Comments, criticism, suggestions very welcome. PhD Tutorial based on
my Dissertatio
Resonant Compton Upscattering in High Field Neutron Stars
The extremely efficient process of resonant Compton upscattering by
relativistic electrons in high magnetic fields is believed to be a leading
emission mechanism of high field pulsars and magnetars in the production of
intense X-ray radiation. New analytic developments for the Compton scattering
cross section using Sokolov & Ternov (S&T) states with spin-dependent resonant
widths are presented. These new results display significant numerical
departures from both the traditional cross section using spin-averaged widths,
and also from the spin-dependent cross section that employs the Johnson &
Lippmann (J&L) basis states, thereby motivating the astrophysical deployment of
this updated resonant Compton formulation. Useful approximate analytic forms
for the cross section in the cyclotron resonance are developed for S&T basis
states. These calculations are applied to an inner magnetospheric model of the
hard X-ray spectral tails in magnetars, recently detected by RXTE and INTEGRAL.
Relativistic electrons cool rapidly near the stellar surface in the presence of
intense baths of thermal X-ray photons. We present resonant Compton cooling
rates for electrons, and the resulting photon spectra at various magnetospheric
locales, for magnetic fields above the quantum critical value. These
demonstrate how this scattering mechanism has the potential to produce the
characteristically flat spectral tails observed in magnetars.Comment: 2 pages, no figures, The proceedings from the Pulsar Conference:
Electromagnetic Radiation from Pulsars and Magnetars will be published in the
Astronomical Society of the Pacific Conference Serie
Kato's theorem and ultralong-range Rydberg molecules
We consider non-adiabatic coupling in the "trilobite"-like long-range Rydberg
molecules created by perturbing degenerate high- Rydberg states with a
ground-state atom. Due to the flexibility granted by the high Rydberg level
density, the avoided crossings between relevant potential energy curves can
become extremely narrow, leading to highly singular non-adiabatic coupling. We
find that the gap between the trilobite potential curve and neighboring
"butterfly" or "dragonfly" potential curves can even vanish, as in a conical
intersection, if the gap closes at an internuclear distance which matches a
node of the -wave radial wave function. This is an unanticipated outcome of
Kato's theorem
Delocalization in two and three-dimensional Rydberg gases
As was recently shown in Ref. 1, many eigenstates of a random Rydberg gas
with resonant dipole-dipole interactions are highly delocalized. Although the
high degree of delocalization is generic to various types of power-law
interactions and to both two and three-dimensional systems, in their detailed
aspects the coherence distributions are sensitive to these parameters and vary
dramatically between different systems. We calculate the eigenstates of both
two and three-dimensional gases and quantify their delocalization throughout
the atoms in the gas using a coherence measure. By contrasting the angular
dependence of the dipole-dipole interaction with an isotropic interaction we
obtain additional information about the generic physical principles underlying
random interacting systems. We also investigate the density of states and
microwave absorption spectra to obtain information about the types of
measurements where these delocalized states play a role, and to check that
these delocalized eigenstates are robust against various types of perturbation