Molecular Line Parameters, Impact on Climate Models and the Quantum-Pascal

Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany

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Published online: 17 February 2026

Abstract

Infrared absorption spectroscopy is one of the most powerful techniques for determining gas compositions. A key input parameter for this method is the absorption line strength, which also has a significant impact on atmospheric and climate models. Line strengths can either be determined experimentally, as demonstrated in this work for three of the strongest absorption lines of carbon monoxide (CO), or calculated using ab-initio theoretical methods. Improving and experimentally validating theoretical line strengths offers the fundamental advantage that complete absorption spectra can be calculated with higher accuracy, leading to more reliable spectroscopic knowledge for climate models. At the Physikalisch-Technische Bundesanstalt (PTB), CO absorption line strengths in the fundamental band in the 4.5 µm wavelength range (R8-R10) were experimentally determined at 296 K, yielding values of 4.452(16)·10^-19, 4.217(16)·10^-19, and 3.851(15)·10^-19 cm molecule^-1 respectively. These results show excellent agreement with the latest theoretical values recently reported by University College London, at sub-percent level. In contrast, line strengths currently used in widely applied databases such as HITRAN deviate from the experimental results by 0.66 %, 1.32 %, and 1.21 %, respectively.