IC/94/295 INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS INNER- AND OUTER-SHELL EXCITATION IN LITHIUM ISOELECTRONIC SEQUENCE S.N. Tiwary and P. Kumar INTERNATIONAL ATOMIC ENERGY AGENCY UNITED NATIONS EDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION MIRAMARE-TRIESTE
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IC/94/295
INTERNATIONAL CENTRE FORTHEORETICAL PHYSICS
INNER- AND OUTER-SHELL EXCITATIONIN LITHIUM ISOELECTRONIC SEQUENCE
S.N. Tiwary
and
P. Kumar
INTERNATIONALATOMIC ENERGY
AGENCY
UNITED NATIONSEDUCATIONAL,
SCIENTIFICAND CULTURALORGANIZATION
MIRAMARE-TRIESTE
IC/94/295
International Atomic Energy Agencyand
United Nations Educational Scientific and Cultural Organization
INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS
INNER- AND OUTER-SHELL EXCITATIONIN LITHIUM ISOELECTRONIC SEQUENCE l
S.N. Tiwary 2
International Centre for Theoretical Physics, Trieste, Italy
and
P. KumarDepartment of Physics, L.S. College BRA Bihar University,
Muzaffarpur, India.
ABSTRACT
The inner-shell excitation Is22s 2Se —* Is2s2 2Se, which leads to autoionization (Augertransition), as well as the outer-shell excitation Is22s 2Se —* Is22p 2P° transitions havebeen investigated in Li, Be+,B2+ and C3+ ions of the lithium isolectronic sequence em-ploying the configuration interaction wave functions for both the initial and final statesinvolved in the transition matrix element. Results are compared with other available the-oretical predictions and experimental observations. Comparison shows that our presenttheoretical results are encouraging.
MIRAMARE - TRIESTE
September 1994
:A part if this work was done while the author was Research Director and Professor,CNRS Laboratory, University of Paris-Sud, Paris and Observatoire de Paris, Meudon,Paris, France.
2Permanent address: Department of Physics, L.S. College BRA Bihar University,Muzaffarpur, India.
1 Introduction
Beyond the ionization limit of atomic systems with several electrons there
generally exist excitation levels corresponding to the excitation not of the
least bound electron but of an inner electron. These core- excited or multiply-
excited levels are degenerate with continuum states of the singly excited
system that is an ionic core in the ground state or low excitation state plus
a free electron. Thus the high lying multiply-excited state can decay easily
by autoionization except for the selection rules which result from parity or
the spin conservation or other reasons.
As a test case for the various effects apparent in the structure of excited sys-
tem, a fairly simple system ought to be chosen. The three- electron systems
provide some neat examples. The lightest alkali-metal atom, i.e., lithium
(Li) and Li-like ions are the best candidates for the study. There has been
growing interest in the inner-shell excitation of atoms and ions from both
experimentalists1'4 and theorists5'25, because inner-shell excitation, in
general, leads to autoionization which plays a very important role in ex-
plaining the structure observed in the total ionization cross section curve
for electron impact.
Accurate absorption optical oscillator strengths for atoms, molecules and
ions in the discrete and continuum regions provide valuable quantitative
information for understanding the high- precision electronic structure of
matter and its interaction with electromagnetic radiation. This information
is of importance in areas of application such as radiation-induced decompo-
sition, biophysics, testing and development of theoretical methods, lithog-
raphy, aeronomy, space chemistry and physics, radiation biology, dosimetry,
health physics, medical physics, radiation protection, astrophysics, atmo-
spheric physics, laser physics, radiation physics, plasma physics, gas dis-
1
i
charge, mass spectroscopy, space research, fusion research, etc. The oscilla-
tor strengths and cross sections provide a sensitive test for atomic structure
calculations. Reliable values of the oscillator strengths and cross sections
are also crucial for the development and evaluation of quantum mechanical
theoretical methods and for the modelling procedures used for various phe-