Excited state structure of neon(2)

Kim, Scott Song-Bom

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Description

Title

Excited state structure of neon(2)

Author(s)

Kim, Scott Song-Bom

Issue Date

1991

Doctoral Committee Chair(s)

Eden, James G.

Department of Study

Electrical and Computer Engineering

Discipline

Electrical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Physical
• Physics, Molecular

Language

eng

Abstract

• Several Rydberg series attributable to transitions originating from the a$\sp{3}\Sigma\sbsp{\rm u}{+}$ metastable state of the neon dimer have been observed by laser excitation spectroscopy in the afterglow of a pulsed corona discharge. Most of the observed bands in the excitation spectrum in the region 25000-34400 cm$\sp{-1}$ are attributed to transitions from the a$\sp{3}\Sigma\sbsp{\rm u}{+}$(v = 0) state, the lowest excited state of Ne$\sb2$. The observed bands are the n = 4-17 members of the np$\pi\ \sp3\Pi\sb{\rm g}\gets$ a$\sp3\Sigma\sbsp{\rm u}{+}$ (0-0) inter-Rydberg transitions, the n = 6-23 members of the np$\sigma\ \sp3\Sigma\sbsp{\rm g}{+}\gets$ a$\sp3\Sigma\sbsp{\rm u}{+}$ (0-0) transitions, and the n = 4 to 6 members of the nf$\lambda$($\sp3\Sigma\sb{\rm g}$, $\sp3\Pi\sb{\rm g}$) $\gets$ a$\sp3\Sigma\sbsp{\rm u}{+}$ (0-0) transitions. An unusual loss of intensity in the Q branches for the higher n member of the np$\pi\ \sp3\Pi\sb{\rm g} \gets$ a$\sp{3}\Sigma\sbsp{\rm u}{+}$ (0-0) transitions and a weak perturbation between the v = 1 vibrational level of the 5f$\sigma\ \sp3\Sigma\sbsp{\rm g}{+}$ state and the 7p$\pi\ \sp3\Pi\sb{\rm g}$, v = 0 level are observed. Also, rotationally resolved spectra of the transitions nf($\sp3\Sigma\sbsp{\rm g}{+}$, $\sp3\Pi\sb{\rm g}$) $\gets$ a$\sp{3}\Sigma\sbsp{\rm u}{+}$ (n = 4-6) show that the rotational structures of the upper states are strongly l-uncoupled; that is, there is an indication of a transition in the angular momentum coupling from Hund's case (b$\sp\prime$) to case(d) with increasing N. A detailed characterization of numerous Rydberg transitions has been made from the rotationally resolved spectra, and molecular constants have been obtained for the states a$\sp{3}\Sigma\sbsp{\rm u}{+}$, nf$\sigma$ $\sp3\Sigma\sbsp{\rm g}{+}$ (n = 4-6), nf$\pi$ $\sp3\Pi\sb{\rm g}$ (n = 4-6), np$\sigma$ $\sp3\Sigma\sbsp{\rm g}{+}$ (n = 10, 12-17, and 19-23), and np$\pi$ $\sp3\Pi\sb{\rm g}$ (n = 4-11, 13-17). From the highly resolved spectra of Ne$\sb2$, the ionization potential of the a$\sp{3}\Sigma\sbsp{\rm u}{+}$ state has been determined (I.P. = 34 409 $\pm$ 2.0 cm$\sp{-1}$).
• The excitation spectrum beyond the X$\sp2\Sigma\sbsp{\rm u}{+}$ Ne$\sbsp{2}{+}$ (v = 0) ionization limit reveals several series of suppressions (windows) superimposed onto predissociative continua which are attributed to the interference effects of the autoionizing superexcited states. The suppressions trace out the (1-0) and (2-0) bands of the np$\pi$ $\sp3\Pi\sb{\rm g}$ $-$ a$\sp{3}\Sigma\sbsp{\rm u}{+}$ Rydberg transitions and are confirmed by the isotopic studies involving $\sp{20}$Ne$\sb2$ and $\sp{22}$Ne$\sb2$. A two-laser, suppression of laser-induced fluorescence experiment has been employed to obtain an equivalent absorption spectrum in these regions; the absorption spectrum shows absorption windows overlapping the LIF suppressions for the series terminating on v = 1 core Rydberg states and absorption peaks overlapping the LIF suppressions for the series terminating on v = 2 of the ion core state. There is a strong indication of Fano interference between the superexcited Rydberg states and several continuum states, which includes the predissociative continuum and the autoionizing continuum.

Type of Resource

text

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Copyright and License Information

Copyright 1991 Kim, Scott Song-Bom

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