Multi-laboratory comparison of 12C16O(3-0) line intensities: towards primary spectroscopic measurements of amount of gas.

Abstract

Lines from the CO (3-0) overtone band in a high-purity CO sample of natural isotopic abundance were measured in five independent laboratories using different experimental techniques: Fourier transform spectroscopy (FTS) in DLR and PTB, cavity ring-down spectroscopy (CRDS) in NIM and NIST, and cavity mode-dispersion spectroscopy (CMDS) in NCU [1]. A set of 10 lines, measured by each of the laboratories, was chosen so that the ratio of the highest and the lowest line intensity was 240:1. In the case of each technique, some of the lines were beyond the optimal intensity range, as the sensitivity of FTS is typically significantly lower than in case of cavity-based techniques such as CRDS and CMDS. The line intensities were determined and compared with the results of the ab initio calculations given in Ref. [2]. A comparison of line intensities determined by different laboratories shows agreement at promille and subpromille levels. Weighted mean experimental values, having relative standard uncertainties of less than 1h, show agreement with theory at 0.5h level. The presented approach shows that combined uncertainties in weighted-mean line intensities (including both statistical and systematic effects) can be reduced by coordinated experiments using multiple primary linear techniques that involve several independent laboratories. References [1] J.T. Hodges, K. Bielska, M. Birk, et al., International Comparison CCQM-P229: Pilot Study to Measure Absolute Line Intensities of Selected 12C16O Transitions, BIPM (in review). [2] K. Bielska, A.A. Kyuberis, Z.D. Reed, et al., Phys. Rev. Lett. 129, 043002 (2022).