Polarization characteristics of Raman scattering for N2, O2, H2O, CO2, and CH4
A.S. Tanichev1,2, I.I. Matrosov1, D.V. Petrov1
1Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
2National Research Tomsk State University, Tomsk, Russia
Keywords: Raman scattering, polarization, depolarization ratio, polarizability invariants, atmospheric air, nitrogen, oxygen, water vapor, carbon dioxide, methane
Abstract
The development of precise light scattering models for lidar sensing of the Earth's atmosphere requires reliable data on the polarization characteristics of molecules. However, for several key atmospheric constituents, such information is either incomplete or entirely absent. In this work, spontaneous Raman spectroscopy is used to experimentally determine the depolarization ratios of the Q-branches of vibrational bands for N2, O2, H2O, CO2, and CH4, which are the main components of atmospheric air. The measurements were performed using a high-sensitivity Raman spectrometer with laser excitation at 532 nm. For the first time, the depolarization ratios were estimated for the CO2 Fermi-triad bands, as well as 2ν2 and 2ν4 overtones of CH4. Based on the obtained data, the ratios of the derivatives of the polarizability tensor invariants for these molecules were determined. The results complement the existing knowledge on the polarization characteristics of atmospheric gas molecules, which is essential for modeling light scattering processes in the Earth's atmosphere.
|
