  In 1986 Alex Dalgarno published a paper entitled "Is Interstellar Chemistry
Useful?" By the middle 1970s, and perhaps even earlier, Alex had hoped that
astronomical molecules would prove to: possess significant diagnostic utility;
control many of the environments in which they exist; stimulate a wide variety
of physicists and chemists who are at least as fascinated by the mechanisms
forming and removing the molecules as by astronomy. His own research efforts
have contributed greatly to the realization of that hope. This paper contains a
few examples of: how molecules are used to diagnose large-scale dynamics in
astronomical sources including star forming regions and supernovae; the ways in
which molecular processes control the evolution of astronomical objects such as
dense cores destined to become stars and very evolved giant stars; theoretical
and laboratory investigations that elucidate the processes producing and
removing astronomical molecules and allow their detection.
