High Resolution Microwave Spetroscopy Of Radioactive Molecules

Author : Satyakumar Nagarajan
Publisher :
ISBN 13 :
Total Pages : 130 pages
Book Rating : 4.:/5 (12 download)

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Download or read book Microwave Spectroscopy written by Satyakumar Nagarajan and published by . This book was released on 2017 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past few decades, microwave spectroscopy has proven to be a very valuable and versatile tool. The important scientific contributions made in this work as well as the variety in the types of problems explored serves as a prime example of such. In the field of chemical sensing, much interest has been drawn towards utilizing microwave spectroscopy to distinguish molecular species. The submillimeter (SMM) spectral region is attractive in terms of being able to obtain a higher degree of specificity compared to that of infrared or optical. This is due to the relatively narrow Doppler line widths that microwave spectral lines exhibit. In this work, we developed a technique called Cavity Based Medium Resolution Spectroscopy (CBMRS), where we used a Fabry-Perot cavity to measure the absolute absorption spectra of large molecules. The spectra of large molecules usually contain broad \enquote{quasi-continuum} features, and measuring these features pose a significant challenge in traditional Doppler limited spectroscopy. This is due to the fact that standing waves that are present in a system are not always discernible from broad spectral features. In CBMRS, we calculated an absorption coefficient at a spectral point by measuring the changes in the widths of the cavity resonances when the cavity was loaded with analyte. This technique allows us to measure an absorption spectrum regardless of the power emitted at the source, the sensitivity of the detector, or the efficiency of coupling power into the cavity. We also successfully implemented CBMRS to function as a chemical sensor by measuring the spectra of of a mixture of gases and identifying the concentrations of the constituent components of the mixture. The SMM region has attracted much interest in astronomy as well. For astronomers interested in finding new molecular species in the interstellar medium (ISM), the SMM proves to be quite favorable. This is due to the fact that microwave radiation can more easily penetrate interstellar dust due to its longer wavelength. Also, the blackbody emission of these clouds tend to be in the temperature range such that the peaks emission falls in the SMM. Studies along these lines have been made possible by the rapid growth in the accessibility of the SMM region over the past couple of decades. Telescopes operating in this regime have also significantly improved in terms of spectral coverage and sensitivity. However, greater sensitivity of telescopes has also brought about a significant challenge. Many of the lines that can be observed belong to a group of molecules called \enquote{astrophysical weeds}. These molecules are abundant but have lines that are difficult to assign due to perturbed rotational transitions and low-lying vibrational states. This has left the quantum mechanical catalogs incomplete. In this work, we used line list catalogs generated in the laboratory to assign lines belonging to astrophysical weed molecules by analyzing intensity-calibrated spectra over a range of temperatures. Using the line list catalogs, we identify lines belonging to these weed molecules in the astrophysical data and determine the physical conditions in which the molecules are found. Then, by using these determined physical conditions, we can predict the spectra of these molecules in the interstellar clouds. This allows astronomers to focus on the remaining features in the astrophysical data to explore further as potential candidates for undiscovered species.