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Research on the properties and interactions of simple atomic and ionic systems

Robert Novick

Published Dec 31, 1972• 0 citations
OpenAlex

Abstract

Simple ionic systems were studied, such as metastable autoionizing states of the negative He ion, two-photon decay spectrum of metastable He ion, optical excitation with low energy ions, and lifetime measurements of singly ionized Li and metastable He ion. Simple atomic systems were also investigated. Metastable autoionizing atomic energy levels in alkali elements were included, along with lifetime measurements of Cr-53, group 2A isotopes, and alkali metal atoms using level crossing and optical double resonance spectroscopy.

Related papers

Auto-Ionizing States in the Alkali Atoms with Microsecond Lifetimes

P. D. Feldman, Robert Novick

Discrete atomic energy levels lying between the first and second ionization potentials which are metastable against both auto-ionization and radiative decay have been observed in the alkali elements. These levels arise from the excitation of an electron from the outermost closed shell of the atom and have characteristic lifetimes in the microsecond region. A beam of metastable alkali atoms is produced by electron bombardment of neutral ground-state atoms and is detected by collecting the charged products of the decay. Stern-Gerlach magnetic-deflection experiments have been performed to show unambiguously that the signals arise from paramagnetic atoms and not from possible stray-photon effects in the apparatus. The excitation energies, electron-bombardment production cross sections, natural lifetimes, and the tentative spectroscopic assignments of these atoms are listed below: The energy and lifetime of the metastable lithium atom are in good agreement with the available theoretical estimates. The metastable states in the heavier alkali atoms are classified in relation to the known ${\mathrm{I}}^{b}$ spectral terms. Magnetic and electric fields have been found to be effective in reducing the lifetime of the metastable atoms. The Zeeman quenching is discussed in a separate paper. The Stark quenching rate has been found to be proportional to the square of the electric field and to increase rapidly with atomic number $Z$. It is suggested that the Stark quenching results from a second-order interaction which involves the product of the electric field and the spin-orbit or other magnetic operators.

Physical Review•Aug 5, 1967•170 citations

Autoionizing States in the Alkali Atoms with Microsecond Lifetimes

P. D. Feldman, Robert Novick

Energy level behavior of metastable alkali atoms against autoionization and radiative decay

Physical Review Letters•Sep 15, 1963•56 citations

Excitation and electronic decay of autoionization states of alkali-earth atoms. Calcium (atomic optically forbidden and ionic states)

A Borovik, I. S. Aleksakhin, A. V. Kuplyauskene

Optics and Spectroscopy•Mar 1, 1982•0 citations

Two-photon ionization of metastable helium

J P Czechanski

There have been relatively few investigations of multiphoton ionization from metastable helium. Of particular interest has been the work of Haberland et al. 1987 and Haberland and Oschwald 1988. In both the 1987 and 1988 papers they have described the two photon ionization of metastable helium. In each of these studies they have reported the occurrence of unexplained structure along the wings of their resonance profiles. Upon the performance of similar measurements by this study, the unexplained structure is not seen and the agreement of the experiment's measurements with the theoretical shape of the resonance curves has been good. To experimentally verify these resonance effects, we have used a tunable dye laser in conjunction with a time of flight mass spectrometer to create and detect ions from metastable helium by two-photon absorption. The use of a metastable state instead of the ground state is advantageous because of its proximity to the ionization continuum and its extended lifetime. Using a metastable state as a starting point for multiphoton absorption requires fewer photons to reach the ionization threshold. The extended lifetime of the state also makes it easy to access experimentally. For helium the singlet metastable state 2$\sp1$S lies at 20.61 eV above the ground level with a natural lifetime of close to a millisecond. Two photons of 501.7 nm and 504.35 nm are required for the ionization processes in resonance with the 3$\sp1$P and the 3$\sp1$D states. This thesis is the accounting of the experimental process involved in the measurement of the dipole and quadrupole resonances of two photon ionization from singlet metastable helium. The study includes the description of the laser, electron gun assembly for metastable helium creation, and the time of flight mass spectrometer. A discussion of the theory of multiphoton processes is included along with the discussion of the data, its reduction and analysis, and a comparison with theoretical prediction. This study has not only involved the acquisition of definitive atomic spectra data sets, but has also established a facility for resonant ionization spectroscopy at The American University.

•Jan 1, 2023•2 citations

State-selective stepwise two-photon detachment study of the ion

H. H. Andersen, Péter Balling, V. V. Petrunin +1 more

The presence of two metastable states in the negative beryllium ion, and , which are connected by an optical transition, offers a unique possibility for gaining new information about this ion. Utilizing resonant, two-photon detachment, combined with resonant-ionization detection of the resulting neutral atoms, we have obtained results yielding the lifetimes of the ( ) and ( ) levels, the fine-structure splittings of the levels, and an improved transition wavelength.

Journal of Physics B Atomic Molecular and Optical Physics•Jun 14, 1996•21 citations

Resonance excitation of autoionizing states in alkali atoms by electron impact

О. О. Боровик

In the work, the main results on excitation and decay processes of autoionizing states in alkali atoms are considered. As follows from the data on excitation dynamics of subvalence shells in an impact energy region from the lowest excitation threshold up to 600 eV, at threshold energies their electron excitation results exclusively from the formation of negative-ion resonances. At mean impact energies, the cascade population processes due to resonance excitation and subsequent radiative decay of the upper states play an essential role for the low-lying autoionizing states. By comparing with theoretical data, the absolute excitation cross sections for autoionizing states and negative-ion resonances were determined. The absolute autoionization cross sections as well as the autoionization contribution to the total single ionization cross section were also determined. Keywords: atom, ion, autoionization, resonances, ionization, effective cross section.

Scientific Herald of Uzhhorod University Series Physics•Nov 25, 2013•0 citations
Simple ionic systems were studied, such as metastable autoionizing states of the negative He ion, two-photon decay spectrum of metastable He ion, optical excitation with low energy ions, and lifetime measurements of singly ionized Li and metastable He ion. Simple atomic systems were also investigated. Metastable autoionizing atomic energy levels in alkali elements were included, along with lifetime measurements of Cr-53, group 2A isotopes, and alkali metal atoms using level crossing and optical double resonance spectroscopy.
Discrete atomic energy levels lying between the first and second ionization potentials which are metastable against both auto-ionization and radiative decay have been observed in the alkali elements. These levels arise from the excitation of an electron from the outermost closed shell of the atom and have characteristic lifetimes in the microsecond region. A beam of metastable alkali atoms is produced by electron bombardment of neutral ground-state atoms and is detected by collecting the charged products of the decay. Stern-Gerlach magnetic-deflection experiments have been performed to show unambiguously that the signals arise from paramagnetic atoms and not from possible stray-photon effects in the apparatus. The excitation energies, electron-bombardment production cross sections, natural lifetimes, and the tentative spectroscopic assignments of these atoms are listed below: The energy and lifetime of the metastable lithium atom are in good agreement with the available theoretical estimates. The metastable states in the heavier alkali atoms are classified in relation to the known Ib{\mathrm{I}}^{b}Ib spectral terms. Magnetic and electric fields have been found to be effective in reducing the lifetime of the metastable atoms. The Zeeman quenching is discussed in a separate paper. The Stark quenching rate has been found to be proportional to the square of the electric field and to increase rapidly with atomic number ZZZ. It is suggested that the Stark quenching results from a second-order interaction which involves the product of the electric field and the spin-orbit or other magnetic operators.
There have been relatively few investigations of multiphoton ionization from metastable helium. Of particular interest has been the work of Haberland et al. 1987 and Haberland and Oschwald 1988. In both the 1987 and 1988 papers they have described the two photon ionization of metastable helium. In each of these studies they have reported the occurrence of unexplained structure along the wings of their resonance profiles. Upon the performance of similar measurements by this study, the unexplained structure is not seen and the agreement of the experiment's measurements with the theoretical shape of the resonance curves has been good. To experimentally verify these resonance effects, we have used a tunable dye laser in conjunction with a time of flight mass spectrometer to create and detect ions from metastable helium by two-photon absorption. The use of a metastable state instead of the ground state is advantageous because of its proximity to the ionization continuum and its extended lifetime. Using a metastable state as a starting point for multiphoton absorption requires fewer photons to reach the ionization threshold. The extended lifetime of the state also makes it easy to access experimentally. For helium the singlet metastable state 2$\sp1$S lies at 20.61 eV above the ground level with a natural lifetime of close to a millisecond. Two photons of 501.7 nm and 504.35 nm are required for the ionization processes in resonance with the 3$\sp1$P and the 3$\sp1$D states. This thesis is the accounting of the experimental process involved in the measurement of the dipole and quadrupole resonances of two photon ionization from singlet metastable helium. The study includes the description of the laser, electron gun assembly for metastable helium creation, and the time of flight mass spectrometer. A discussion of the theory of multiphoton processes is included along with the discussion of the data, its reduction and analysis, and a comparison with theoretical prediction. This study has not only involved the acquisition of definitive atomic spectra data sets, but has also established a facility for resonant ionization spectroscopy at The American University.
In the work, the main results on excitation and decay processes of autoionizing states in alkali atoms are considered. As follows from the data on excitation dynamics of subvalence shells in an impact energy region from the lowest excitation threshold up to 600 eV, at threshold energies their electron excitation results exclusively from the formation of negative-ion resonances. At mean impact energies, the cascade population processes due to resonance excitation and subsequent radiative decay of the upper states play an essential role for the low-lying autoionizing states. By comparing with theoretical data, the absolute excitation cross sections for autoionizing states and negative-ion resonances were determined. The absolute autoionization cross sections as well as the autoionization contribution to the total single ionization cross section were also determined. Keywords: atom, ion, autoionization, resonances, ionization, effective cross section.