Merging Complementary Techniques in Laboratory Spectroscopy for Remote Sensing Applications

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Molecular spectroscopy allows us to identify molecules in locations not easily accessible, such as the upper layers of the Earth’s atmosphere, interstellar clouds, and the atmospheres of other planets, comets and of cool stars. It is the shape of a spectral line that provides a “window” for us to look inside the mechanism governing the absorption and emission of radiation and interpret them beyond the classical pictures accepted so far. In addition to molecular identification and quantitation, spectroscopic techniques can provide information on the physical properties of remote environments. This is the basis of remote sensing which is used extensively in atmospheric studies. Extremely precise spectral measurements of a line shape can help us understand fundamental processes of molecular dynamics and in the interpretation of remote sensing data. Extracting information from remote sensing spectra requires quantum state-resolved data (line positions, intensities, and shapes) from both laboratory spectroscopy and from theoretical models. There is an increasing need for highly accurate compilations of line parameters of molecules that are common in various astrophysical environments including exoplanet atmospheres. This is being driven by the availability of ever increasingly high-resolution telescopes and instruments, including space-based such as Herschel, the future JWST, plane-based such as SOFIA, and ground based such as ALMA. For many of the molecules of interest, the line lists need to be able to span a large temperature range since they exists in different environments that span a wide temperature range. I propose to investigate N2O3, an undertaking that is most challenging because of the chemical instability of N2O3 and the fact that combinations of various experimental techniques and theoretical modelling, including ab initio calculations, are required. The goal of the proposed research is to obtain more accurate information on the low lying infrared bands in asymmetric- and possibly symmetric-N2O3 by recording, for the first time, the high resolution far-infrared spectrum of a cooled mixture of NO and NO2/N2O4. The concentration errors in the laboratory experiments can be overcome by measuring simultaneously, and on the same sample, suitable IR absorptions around 8-10 µm with a laser spectrometer that will be re-located from our lab for the experiments, and to determine the actual concentration by simultaneously recording the pure rotational spectrum by high resolution Fourier Transform Spectroscopy (FTS). Therefore, the successful completion of the project requires two experimental techniques to be combined: Fourier Transform Infrared Spectroscopy and diode laser spectroscopy. Part of this proposal is also a near infrared study of methane for planetary atmospheres of cold giant planets and hot exoplanets. I propose to use a combination of theory and high-resolution experiments to determine highly accurate line parameters of H2-broadened methane features in the K band. The measurements will focus on a) weaker lines between 4450 and 4700 cm-1, using new spectra at cold temperatures (215 – 296 K) for cold giant planets, and b) stronger lines in the 4300 – 4450 cm-1 using spectra at elevated temperatures (296 – 350 K) for extra-solar planets (e.g. hot-Jupiters). The measured H2-broadened linewidths, pressure-shifts, and temperature dependence exponent coefficients will enable accurate line-by-line calculations for a wide range of temperatures. This study will support analyses of planetary and exoplanetary atmospheres using ground-, and space-based observations (present and future) and will allow the theorists to extend their “global analysis of methane”.