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

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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 An m values have been measured relative to that of the longest-wavelength resonance multiplet (λ=165.7 nm) and subsequently have been normalized to an absolute scale by recent results of lifetime measurements of the upper levels 3sP∘3 of this multiplet. Because the 3sP∘3 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 An 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 An m values between the longest-wavelength resonance multiplet λ=165.7 nm and the prominent visible line λ=505.21 nm was determined. In this manner a set of absolute CIAn m values in the visible range was established based also on the lifetime of the 3sP∘3 levels. An m was found to be (1.4 ± 0.3) × 106 s−1 for λ=505.21 nm.