Fourier-transform VUV spectroscopy of $^{14,15}$N and $^{12,13}$C

TL;DR

This study used Fourier-transform spectroscopy at the Soleil synchrotron to measure vacuum ultraviolet transitions in atomic nitrogen and carbon, revealing precise energy levels, isotope shifts, and a small offset from NIST data.

Contribution

The paper provides highly accurate VUV absorption measurements of nitrogen and carbon isotopes, improving existing data and confirming theoretical isotope shift predictions.

Findings

Measured nitrogen transitions with 0.025 cm⁻¹ accuracy.

Identified a -0.04 cm⁻¹ offset from NIST database values.

Determined isotope shifts for nitrogen and carbon transitions.

Abstract

Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For $^{14}$N transitions from the $2s^22p^3\,^4$S$_{3/2}$ ground state and from the $2s^22p^3\,^2$P and $^2$D metastable states were determined in the $95 - 124$ nm range at an accuracy of $0.025\,\mathrm{cm}^{-1}$. Combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveal an overall and consistent offset of -0.04 \wn\ from values reported in the NIST database. %The splitting of the $2s^22p^3\,^4$S$_{3/2}$ -- %$2s2p^4\,^4$P$_{5/2,3/2,1/2}$ The splittings of the $2s^22p^3\,^4$S$_{3/2}$ -- $2s2p^4\,^4$P$_{J}$ transitions are well-resolved for $^{14}$N and $^{15}$N and 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 $2s^22p^2\,^3$P$_{J}$ and $2s^22p3s\, ^3$P$_{J}$ excited states at $165$ nm are measured for both $^{12}$C and $^{13}$C isotopes.