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DeWayne Halfen - University of Arizona

Wednesday, May 27 – 10:45-11:30AM


“Investigating the Chemistry of the Universe: Combining the Power of Rotational Spectroscopy and Radio Astronomy”


To date, over 145 different chemical compounds have been securely identified in the gas phase in interstellar space. These identifications have been possible because of high-resolution laboratory spectroscopy measurements, coupled with the remote sensing capabilities of radio astronomy. Because the interstellar medium is cold (T ~ 10 - 100 K) and not very dense (n ~ 103 - 106 particles/cc), rotational energy levels of molecules are predominantly populated, as opposed to vibrational or electronic. Thus, laboratory measurements of potential interstellar species have focused on rotational spectroscopy with accuracies of one part in 107 - 108. Direct absorption techniques, Fourier transform microwave spectroscopy, and velocity modulation methods are routinely used for such measurements. Also exotic molecular syntheses are often required. Determination of the rotational transition frequencies provides the “fingerprint” pattern by which an individual species can be identified in the interstellar medium. Heterodyne mixer detectors at radio telescopes can be tuned to these frequencies to search for emission from a given molecule from an astronomical source. This combined approach has recently resulted in the identification of several “transient” interstellar molecules, including CCP, HSCN, and AlOH. Methods used to study these molecules in the laboratory will be discussed, as well as those of radio telescopes.