Vacuum Ultraviolet Fourier-transform Spectroscopy of 16O and 18O

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jats:titleAbstract</jats:title> jats:pA spectroscopic study of atomic oxygen (O jats:sci</jats:sc>) is performed using the Fourier-transform vacuum ultraviolet (VUV) spectrometer at the Dichroïsme Et Spectroscopie par Interaction avec le Rayonnement Synchrotron beamline of the SOLEIL synchrotron. Transition frequencies of O jats:sci</jats:sc> lines in the range between 76,000 and 151,000 cmjats:sup−1</jats:sup>, corresponding to wavelengths between 665 and 1306 Å, are presented. In the wavelength window a data set of 208 lines is obtained for which line centers were determined at an accuracy of ≤0.035 cmjats:sup−1</jats:sup>, verified through a comparison with previous VUV-laser spectroscopy at an accuracy of 0.008 cmjats:sup−1</jats:sup>. Transitions to upper states belonging to several jats:italicns</jats:italic> and jats:italicnd</jats:italic> Rydberg series that converge to the jats:sup4</jats:sup>Sjats:sub3/2</jats:sub>, jats:sup2</jats:sup>D, and jats:sup2</jats:sup>P ionization limits are presented. Besides studies on the main jats:sup16</jats:sup>O isotope, measurements of the jats:sup18</jats:sup>O isotope are also performed, for which an enriched sample of jats:sup18</jats:sup>Ojats:sub2</jats:sub> gas is used. A least-squares optimization analysis is performed after merging the present new data set with some relevant accurate literature data to extract a list of level energies at high accuracy. When comparing with the database of the National Institute of Standards and Technology, good agreement is found for levels with low principal quantum numbers jats:italicn</jats:italic> ≤ 7 or below excitation energies of 108,000 cmjats:sup−1</jats:sup>; however, significant deviations were found for levels with jats:italicn</jats:italic> > 7. The main result of the present study is the realization of an improved data set of transition frequencies and level energies for O jats:sci</jats:sc>, with its usefulness demonstrated in a comparison with high-resolution astronomical spectra showing absorption in the line of sight to distant quasars.</jats:p>

5102 Atomic, Molecular and Optical Physics, 51 Physical Sciences
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The Astrophysical Journal Supplement Series
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American Astronomical Society
Royal Society University Fellowship (UF150281)
UKRI ∣ Science and Technology Facilities Council (STFC) (ST/T000244/1)