The first observation of interstellar molecules occurred in 1937, with the discovery of sharp absorption lines in the ultraviolet spectra of several stars.1 These features were found to be associated with the presence of interstellar CH+, CH and CN. These features, which were apparent in the spectra of a large number of bright stars, were essentially the only evidence for the existence of interstellar molecules until 1963, when Weinreb et al.2 observed absorption at 1665 MHz against several continuum sources. This feature was found to be associated with transitions between the ground state Λ-doublet levels of OH.
KeywordsGalactic Center Kinetic Temperature Synchronous Detector Parametric Amplifier Interstellar Molecule
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