I am a microwave spectroscopist and have worked with this magnificent spectroscopic technique for more than 40 years, almost from time it was used to identify the first interstellar polyatomic molecule, NH3. I have witnessed its increasing application to the study of the chemistry of the Universe.
It is changes in the rotation energy of a compound that give rise to a microwave spectrum. Only gaseous compounds have distinct microwave spectra. Microwave spectroscopy is above all characterized by its superior accuracy and resolution. There is nothing more accurate. Microwave spectra from the interstellar space are recorded by radio astronomy observatories. Comparison of the observed absorption or emission spectral lines from interstellar space with laboratory spectra leads to identification, or rejection, of an interstellar candidate molecule. The vast majority of compounds that have been found in interstellar space have been identified in this way. Right now, about 150 different compounds have been found in space. This number is steadily increasing.
The molecules are normally found in interstellar clouds, such as, for example, the Orion cloud. The interstellar compounds are present not only in the Milky Way, but have been found in galaxies that are as far away as 10 billion light years. Not only “ordinary” compounds with closed electron shells have been found. In fact, a number of radicals, cations and anions have also been identified. The interstellar space has proved to have an unusual, almost exotic chemistry, which has been a true challenge to chemistry.
It is not possible to identify a new species in space unless you have its analyzed laboratory spectrum. This is where we come in. We have a modern Stark modulated microwave spectrometer, which operates in the 7 – 80 GHz spectral range. Our work has been to assign microwave spectra of molecules, especially compounds of astrobiological interest, so that they can be used by radio astronomers in an attempt to identify these species in space. We have been successful in several cases, whereas no identification has been made for a number of other molecules, but the last word has hardly been said. Improved radio astronomical techniques and observatories placed in space or on the moon will provide a wealth of new and improved spectra from space. It is therefore predicted that many more interstellar compounds will be identified by the use of microwave spectra that have already been assigned in the laboratory. The new and improved observation platforms will create an increasing demand for high resolution rotational spectra. Microwave spectroscopy will have plenty to do.
The reaction mechanisms of interstellar chemistry are often poorly understood. Fortunately, modern quantum chemical calculations can provide useful insight in the generation and destruction of interstellar species. Our laboratory is also involved in the quantum chemical modeling of interstellar reactions. Quantum chemical calculations have already become important in astrochemistry and its role is predicted to increase considerably in the coming years. Further information is found on my home page
