FIGURE 2.1 Typical spectrum of a dense molecular cloud, Sgr B2(N), obtained in a portion of the 71- 238 GHz band, using the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory using a single-sideband (SSB) receiver covering a 1 GHz band. Integration time is 2 hours. A large fraction, but not all, of the molecular lines have been labeled on the spectrum. “U” indicates unidentified lines. Because radio telescopes use heterodyne receivers with multiplexing spectrometers, spectral resolution as high as 1 part in 108 can be achieved, particularly in cold, quiescent astronomical sources. This resolution is invaluable for chemical identification of molecules, and for investigations of velocity structure in astronomical objects. SOURCE: Lucy Ziurys, University of Arizona.

are invaluable in investigating galactic chemical evolution and nucleosynthesis in stars. Maser action often occurs in certain molecules in star-forming regions and in envelopes of evolved stars, such as in SiO or CH3OH. Observations of maser lines provide information on small-scale structure and time variability of emitting sources.

The 71-238 GHz region also covers the premier spectral windows for astrochemistry. Many new interstellar molecules are discovered by observations at these frequencies, as illustrated by the recent identification of CCP, PO, HSCN, AlO, and AlOH. It is naturally difficult to predict a priori the transition frequencies of any possible new molecule. Therefore, protecting given lines does not fully cover the science that comes from observations in these bands.

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