Measurement of transition probabilities of C I multiplets in the visible and vacuum-ultraviolet spectral region utilizing arc-plasma emission and synchrotron-calibrated radiometric transfer standards

Abstract

The vuv transition probabilities of C I have been measured in emission with a high-current, wall-stabilized are operated in a mixture of argon, carbon dioxide, and hydrogen at atmospheric pressure. A radiometric technique has been performed utilizing synchrotron-calibrated gas discharge lamps (deuterium lamps) as spectral radiance standards. At present, the number density of the emitting carbon atoms of the used multicomponent plasma cannot be determined by plasma-spectroscopic means with satisfactory reliability. Therefore, the ${A}_{n m}$ values have been measured relative to that of the longest-wavelength resonance multiplet ($\ensuremath{\lambda}=165.7$ nm) and subsequently have been normalized to an absolute scale by recent results of lifetime measurements of the upper levels $3s^{3}P^{\ensuremath{\circ}}$ of this multiplet. Because the $3s^{3}P^{\ensuremath{\circ}}$ levels decay with a significant transition probability only to the ground-state level, branching ratios need not be considered when converting the lifetime to the absolute ${A}_{n m}$ value. The transition probabilities determined on this basis disagree in some cases with previous experimental and theoretical results presently adopted as the most-reliable values. A maximum deviation by a factor of approximately 2 has been observed. Using the synchrotron-calibrated spectral radiance standards, the ratio of the ${A}_{n m}$ values between the longest-wavelength resonance multiplet $\ensuremath{\lambda}=165.7$ nm and the prominent visible line $\ensuremath{\lambda}=505.21$ nm was determined. In this manner a set of absolute ${\mathrm{C}}_{\mathrm{I}}{A}_{n m}$ values in the visible range was established based also on the lifetime of the $3s^{3}P^{\ensuremath{\circ}}$ levels. ${A}_{n m}$ was found to be (1.4 \ifmmode\pm\else\textpm\fi{} 0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ ${\mathrm{s}}^{\ensuremath{-}1}$ for $\ensuremath{\lambda}=505.21$ nm.