Centimeter-wave spectroscopy is one of the most sensitive and convenient methods to detect and spectrally characterize many molecules of astronomical interest, even if the molecule is extremely light, and its most intense rotational transitions lie in the mmw, sub-mmw, or THz bands. Fourier transform microwave spectroscopy combined with supersonic molecular beams, either in a high-Q cavity resonator or by broadband chirped pulsed methods, have been used with good success to detect a wide variety of astronomical species, including radicals, carbenes, and molecular ions. Such studies routinely yield highly accurate spectroscopic constants, allowing searches for rotational transitions to be undertaken with little uncertainty or ambiguity at higher frequencies. Owing to the large number of interfering background lines observed in the millimeter and THz bands in laboratory discharge cells, identifications are greatly simplified when rotational constants derived from the centimeter-wave measurements are already in hand. These studies also provide derived abundances and experimental conditions, so that subsequent laboratory investigations can be undertaken with confidence, either independently or by optimizing and monitoring the cm-wave lines.  This talk will illustrate specific examples of how cm-wave measurements have directly assisted THz work.  The prospects for further improvements and capabilities will also be discussed.

Centimeter-wave rotational spectroscopy: A stepping stone to the FIR and beyond

247th National Meeting (2014)

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