At present, more than 100 different chemical species have been detected in interstellar space, primarily in giant gas clouds scattered throughout our Galaxy. The objectives of my research are to study these molecules and their chemistry via an interdisciplinary approach that involves both high resolution molecular spectroscopy in the laboratory and observational techniques of radio astronomy. The work primarily concerns (1) laboratory spectroscopy of potential interstellar molecules and (2) observational studies of these molecules using radio telescopes.

The aim of the laboratory research is to measure the gas-phase rotational spectra of the species of interest in the millimeter/ sub-millimeter region of the electromagnetic spectrum (^~60-600 GHz). This goal requires design and construction of our own direct absorption spectrometer systems. Also, the physical conditions in interstellar gas are quite different from those of Earth, being much colder (10-100 K) and having significantly lower densities (^~10⁴-10⁶ particles/cc). Hence, interstellar molecules are usually species that are short-lived here on Earth, namely free radicals and molecular ions. Therefore, part of the laboratory work concerns developing exotic synthetic techniques for creating these transient species in detectable concentrations. Of interest are small molecules that contain the cosmically abundant metals such as magnesium, iron, and aluminum. Up to the present, we have succeeded in recording the spectra of a variety of metal-bearing hydride, hydroxide, cyanide, acetylide, methyl, and carbide radicals, including MgOH, AlCH₃, MgCN, CaCCH, FeF, and FeC. (See Figure 1). Almost all of these species have unpaired electrons, and thus their spectra exhibit fine and hyperfine splittings. Analysis of such data requires a detailed knowledge of quantum mechanics and the coupling of angular momentum.

The ratio astronomy aspect of this research program principally concerns the detection of new interstellar molecules, which is achieved by observing their pure rotational spectra using millimeter and sub-mm wave telescopes. Thus, the measurements obtained in our laboratory are directly employed in the identification of these species in astronomical sources. For example, we have recently detected a new interstellar molecule, MgCN, towards the late-type carbon star IRC+10216. Observations of the molecules are conducted at various sites, including the National Radio Astronomy Observatory 12 meter telescope located on Kitt Peak in Arizona, the IRAM 30 m telescope near Granada, Spain, and the new Sub-millimeter Telescope (SMT) on Mount Graham, also in Arizona. From the interstellar spectra, the abundance and distribution of a given chemical species can be determined. The combined laboratory and observational data provide unique insights into astrochemical processes that occur in the interstellar medium.