Abstract
Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For 14N, transitions from the 2s22p34S3/2 ground state and from the 2s22p32P and 2D metastable states were determined in the 95–124 nm range at an accuracy of 0.025cm−1. The combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveals an overall and consistent offset of −0.04 cm−1 from values reported in the NIST database. The splittings of the 2s22p34S3/2 – 2s2p44PJ transitions are well-resolved for 14N and 15N and the isotope shifts determined. While excitation of a 2p valence electron yields very small isotope shifts, excitation of a 2s core electron results in large isotope shifts, in agreement with theoretical predictions. For carbon, six transitions from the ground 2s22p23PJ and 2s22p3s3PJ excited states at 165 nm are measured for both 12C and 13C isotopes.
Highlights
The determination of level energies in first row atoms critically relies on accurate spectroscopic measurements in the vacuum ultraviolet (VUV) region below the atmospheric absorption cutoff.The present study applies a unique Fourier-transform spectroscopic instrument in combination with synchrotron radiation to access this wavelength range at high resolution and accuracy for improving the atomic level structures of N and C atoms, including isotopic effects.The currently available level energies and line classifications for the N atom, compiled in the comprehensive NIST database [1], mostly originate from the work of Eriksson and coworkers from the late 1950s in combination with the work by Kaufman and Ward [2]
Two different sets of lines are measured for N I, lines in excitation from the 4 S3/2 ground state and lines excited from 2 D J metastable states produced in the plasma
Accurate measurements of transition energies in nitrogen and carbon atoms were obtained at an absolute accuracy of 0.025 cm−1 using VUV Fourier-transform spectroscopy with a synchrotron radiation source
Summary
The currently available level energies and line classifications for the N atom, compiled in the comprehensive NIST database [1], mostly originate from the work of Eriksson and coworkers from the late 1950s in combination with the work by Kaufman and Ward [2]. Eriksson measured N I (neutral nitrogen) transitions between 113.4–174.5 nm at about 0.1 cm−1 accuracy and constructed the atomic level structure, including information on transitions between excited states in the visible and IR region [3,4]. Kaufman and Ward measured the 2p3 2 D J – 3s 2 P J and 2p3 2 P J – 3s 2 P J transitions to extend the knowledge of the level structure of the ground configuration at better than 0.04 cm−1 accuracy [2], including the forbidden transition 4 S1/2 – 2 P J measured by Eriksson. Salumbides et al [9] measured
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