Subpromille measurements of H2 absorption spectra near 1.2 μm

The molecule hydrogen is the most abundant neutral molecule in the universe and dominates the atmosphere of gas giants in the solar system and beyond. Laboratory-measured spectral data of the hydrogen molecule, including transition absorption (?) frequencies, intensities, and related temperature-/pressure-dependent spectroscopic parameters, are the basis for modeling the planetary atmospheres [1].

The present work is based on two high precision cavity enhanced spectroscopy methods. Both absorption and dispersion spectra were recorded with the same frequency-stabilized cavity-enhanced spectroscopy instrument referenced to an optical frequency comb. Doppler-broadened spectra of the first overtone Q(1) line of the H2 molecule near 1.2 µm were measured in the range of 20-80 kPa. The spectrums were fitted by the Hartmann-Tran profile (HTP) [2], which is suitable for molecule hydrogen analysis. The line intensities obtained by the two methods reached an accuracy of 0.15%, and they agree well with theoretical results [3]. It is the first time that subpromille measurements of a rovibrational transition of the hydrogen molecule have been performed with two different methods. The work paves the way for SI-traceable high-precision molecular density measurements based on laser spectroscopy.

The experimental detail and the data analysis results will be presented and discussed.

 

Acknowledgments

This work was jointly supported by the National Natural Science Foundation of China (Grant Nos. 12393825, 12393822, 22327801, 22241302), the Innovation Program for Quantum Science and Technology (Grant Nos. 2021ZD0303102, 2022YFF0606500), and the Chinese Academy of Sciences (Grant No. YSBR-055).

References

[1] Liu, Q. H., Tan, Y., Cheng, C. F., & Hu, S. M. (2023). Precision spectroscopy of molecular hydrogen. Physical Chemistry Chemical Physics, 25(41), 27914-27925.

[2] Konefał, M., Słowiński, M., Zaborowski, M., Ciuryło, R., Lisak, D., & Wcisło, P. (2020). Analytical-function correction to the Hartmann–Tran profile for more reliable representation of the Dicke-narrowed molecular spectra. Journal of Quantitative Spectroscopy and Radiative Transfer, 242, 106784.

[3] Komasa, J., Puchalski, M., Czachorowski, P., Łach, G., & Pachucki, K. (2019). Rovibrational energy levels of the hydrogen molecule through nonadiabatic perturbation theory. Physical Review A, 100(3), 032519.