The chemistry of the interstellar medium

Abstract
There has been a dramatic advance in our appreciation of the richness of the molecular component of the interstellar medium, mainly brought about by combining laboratory spectroscopic measurements with radioastronomy search programmes. We now know that vast hordes of molecules lurk deep in the black clouds strewn among the stars of the Galaxy. They range from commonplace small species such as water and carbon monoxide through organic ones such as alcohol and formaldehyde to highly reactive ions and free radicals which are intermediates in the production of more complex molecules. The study of the microwave and infrared signals from these molecules has revealed, for the first time, the intimate details that surround the birth of a star. Some intriguing and rather exotic molecules, consisting primarily of carbon atoms connected in long chains, have also been identified. Not only are these curious molecules to be found in the cold tenuous dark clouds but they are also to be found streaming out of carbon-rich stars into the surrounding interstellar medium. Such stars also appear to be emitting copious quantities of dust. Laboratory experiments, stimulated by these observations, have led to the discovery of the hollow spheroidal carbon molecule, C 60 buckminsterfullerene. This discovery has not only provided the key to the mechanism of formation of small carbon particles (such as soot) but also the first detailed understanding of their structure. These processes and the species that result may be directly related to those involved in the formation of the primordial macroscopic particle.