Laboratory Spectroscopy of Highly-Reactive Molecules of Astrophysical Interest
Michael C. McCarthy
Understanding the chemical composition in the interstellar medium can provide much insight into a variety of astrophysical processes, allowing one to derive important physical properties such as mass loss, temperature, density, fractional ionization, etc. Many of the key chemical intermediates found in space are highly reactive or unstable species, generally unknown or unfamiliar on Earth, such as radicals, carbenes, and positively and negatively-charged ions. Unambiguous astronomical detection of these reactive intermediates frequently requires highly accurate measurements of their rotational spectra throughout the radio band. Using highly sensitive laboratory instrumentation and production techniques developed at SAO, such measurements are undertaken, yielding precisely rest frequencies to guide dedicated radio astronomical searches for new molecules.
What are the key chemical intermediates in astronomical sources? What methods and techniques can be used to detect this species in the laboratory? How can these intermediates be used to provide new insight into astrophysical process?
Chemically unstable molecules of astronomical interest are produced and detected in the radio band using custom instrumentation. Laboratory searches are often undertaken in collaboration with leading theoretical groups here and abroad because computational predictions serve as a useful guide to experiment. Target reactive species are synthesized by applying an electrical discharge to a mixture of precursor gases, as the gas mixture rapidly expands to form an ultra-cold molecular beam. Fourier transform microwave spectroscopy is used in the centimeter-wave band to conduct spectral surveys at frequencies predicted by theory. Follow-up investigations to confirm the carrier of the rotational lines or to extend the frequency range of the laboratory measurements are often undertaken as part of this effort.