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Infrared laboratory spectroscopy of atmospheric gases

Infrared spectroscopy provides a tool for measuring the interaction of a molecule with different wavelengths of infrared light. Infrared spectra act as molecular fingerprints and are used to retrieve atmospheric trace gas concentrations and derive climate metrics.  Transitions between rotational and vibrational energy levels result in discrete absorption features. Heavy molecules with large moments of inertia and small rotational constants, have a high density of rotational-vibrational transitions, which can be measured as broader absorption cross-sections.

This talk will discuss two spectroscopic sample cells used to measure absorption cross-sections in the laboratory. The first is a 10-cm cell that has been used to measure perfluoro-n-heptane and perfluoro-n-octane absorption cross-sections. We derived the radiative efficiency and global warming potential climate metrics using the measured cross-sections. The radiative efficiency measures the change in net downward flux at the tropopause due to the addition of greenhouse gas. The global warming potential quantifies the contribution of a given substance to global warming relative to an equivalent mass of carbon dioxide over a given period, usually 100 years. Our results show that perfluoro-n-heptane and perfluoro-n-octane are two highly potent greenhouse gases.

The second cell is a multi-pass White cell that is currently being commissioned. Once complete, the cell will be used to measure the absorption cross-sections of weakly interacting species. We will present the progress on the optical alignment of this cell. 

Host: Christian DiMaria
Event series  Brewer-Wilson Seminar Series