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Ann. Rev. Phys. Chem. 1981, 32:103-38 ) } /

INTERSTELLAR CHEMISTRY: #2724
Exotic Molecules in Space’

Sheldon Green

NASA Goddard Institute for Space Studies,
2880 Broadway, New York, New York 10025

INTRODUCTION

The field of interstellar chemistry had its beginnings in 1968 with the
microwave detection of the first interstellar polyatomic molecule, ammo-
nia. Since then over 50 species have been identified in space (Table 1) (1).
Before this it had been thought that molecular processes (as opposed, for
example, to atomic and nuclear processes) played little or no role in astro-
physics. The wealth of molecular radioastronomical data that has accu-
mulated in the last decade demonstrates quite forcefully that this is not
true. Analysis of this data requires information about a number of molec-
ular properties and processes which fall traditionally into the area of
physical chemistry. However, because conditions in interstellar space are
so different from those which are normally attained in the laboratory—
essentially zero pressure and nearly zero temperature—attempts to under-
stand interstellar chemistry have stretched the limits of current physical
chemical knowledge. The flow of information between molecular radio-
astronomy and physical chemistry has therefore been reciprocal, and it is
likely to remain this way for some time.

Although still quite young, the field of interstellar chemistry has uncov-
ered a remarkably rich and varied phenomenology that has already made
important contributions to our understanding of both astronomy and
chemistry. In fact, the field is much too broad to be adequately surveyed
within the space limitations of this article. Molecular radioastronomical
observations have provided important new information for astrophysics,
including the morphology and thermal balance of the interstellar medium,
clues to stellar evolution, and information about cosmic isotope ratios that

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