The Lab between the Stars.

In space, where a hydrogen atom might fly for a million years before finding a soul mate, the opportunities for significant chemistry might appear a little on the limited side. Nothing could be further from the truth. The Universe is a big place and one thing which is not in short supply is time. Most chemistry, despite the impression that is given to students by university courses, occurs not on Earth but in the yawning chasm between the stars. There is mode alcohol, for instance, in the aver­age molecular gas cloud than has ever been distilled in the entire history of the human race.

Granted, " astrochemistry" may not be quite as complex as Earthbound chemistry, whether in the laboratory, industry or living organisms. Never­theless, it is far more intricate than anyone would have guessed even a few decades ago. It embraces esoteric processes, the likes of which are never seen in the high-density environment on Earth. Furthermore, astrochem­istry actually orchestrates a great deal of what goes on in the Universe, which is precisely what is detailed in The Chemically Controlled Cosmosby Thomas Hartquist of the Max Planck Institute for Extraterrestrial Physic in Munich and David Williams of University College London.

Molecules form, the authors tell us, whenever the temperature of matter falls below 3000°C. And since most of the Universe is either colder than this, or has been colder than this at least once since the big bang, molecules have been a ubiquitous feature of the cosmos through­out most of its history. The first time the temperature dipped beneath 3000°C, say Hartquist and Williams, was in the rapidly expanding fire­ball of the big bang about a million years after the moment of creation. Chemistry in this remote epoch was rudimentary because very few elements heavier than hydrogen and helium were forged in the fiery furnace of the big bang. Nevertheless, molecular hydrogen played a crucial role in cooling the cores of giant gas clouds so that they could shrink under their own gravity.

Without its ability to radiate away heat generated during the proc­ess, say Hartquist and Williams, pressure from the hot gas would have prevented galaxies like our own Milky Way from congealing from the stuff of the big bang. Molecules have the ability to remove heat from a gas because when they collide with each other some of their energy of motion is inevitably converted into internal energy. This energy can later be shed in the form of photons.

A molecule can be thought of as a collection of balls connected by springs. The whole structure can vibrate and rotate and, when it is buffeted by other molecules, can be made to vibrate or rotate even faster. Because the laws of quantum mechanics permit only certain rates of vibration and rotation, when the molecule sheds energy by emitting photons it does so at only certain characteristic wavelengths, usually in the infrared of millimetre wave region of the spectrum. For instance, carbon monoxide, the most abundant molecule in space after molecu­lar hydrogen, emits a characteristic spectral " line" at a wavelength of 2-6 millimetres.

So far, astronomers have detected the characteristic spectral signa­tures of almost 100 different interstellar molecules and radicals. And this number does not include variant forms of many of these molecules in which a relatively rare isotope, such as deuterium, substitutes for a more common one like hydrogen.

Astronomers have found the carbon monoxide molecule, for ex­ample. It has been detected in interstellar clouds with all possible com­binations of not only carbon-12 and carbon-13 but also oxygen-16, xygen-17 and oxygen-18. Each of the six separate forms of carbon monoxide exhibits the slightly different masses of its constituent at­oms.

In space, you can find methanol in literally astronomical quanti­ties. It is so dilute that in even the densest molecular clouds it would be necessary to sift through cubic kilometres of space to fill a single glass.

The simple amino acid glycine exists in space as well. It was discov­ered two years ago in Sagittarius B2, the giant molecular cloud at the heart of our Galaxy in which virtually every known space molecule has been found at one time or another.

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