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

Precise determinations of gas parameters, such as absorption line strengths, are critical for validating theoretical models and ensuring the reliability of climate simulations. At the Physikalisch-Technische Bundesanstalt (PTB), high-precision spectroscopic measurements are conducted on various molecular species. Recent measurements of the strongest absorption line strengths in the fundamental band of carbon monoxide (CO) show excellent agreement with the latest theoretical predictions, thereby enhancing confidence in molecular databases. Key experimental parameters influencing accuracy include the optical path length, gas pressure, and temperature. The 2019 redefinition of the International System of Units (SI) has enabled a new approach to pressure realization based on gas density, offering significant advantages in precision. This method, known as the Quantum-Pascal, has been developed by leading national metrology institutes and is now being practically implemented, particularly through Fabry-Perot Refractometry (FPR). FPR determines pressure by assessing shifts in laser frequency which is a quantity measurable with extremely low uncertainty. Furthermore, FPR-based pressure realization requires precise gas temperature determination, which is crucial for density-based pressure assessments using the equation of state. The Quantum-Pascal has the potential to significantly improve the reliability of gas analysis via absorption spectroscopy by improving the accuracy of pressure and temperature measurements. In this presentation, we will show the current results of CO line parameters and related measurement details. We will also point out how the Quantum-Pascal can improve the assessment of molecular line parameters, which are fundamental to climate models.