NON-EQUILIBRIUM PROCESSES OF ORGANIC SUBSTANCES ’ SYNTHESIS IN INTERSTELLAR GAS-DUST CLOUDS

At the present time evidence continues to demonstrate the existence of organic molecules in interstellar space. Astronomical observations have revealed interstellar clouds of microscopic (micron-sized) dust grains (1%) and gas concentrates of about 20-30 % of galactic matter (Chang, 1981). In the discussion below, we distinguish two classes of interstellar clouds: (i) diffuse clouds, which generally consist mostly of atomic rather than molecular hydrogen, and (ii) dense clouds, in which the hydrogen is overwhelmingly molecular. A gross distinction between the two is made when the optical extinction of the dust is unity. In diffuse clouds, which can be examined by line absorption of background visible and UV stellar radiation, gas densities are less than a few hundred atoms cm-3; gas temperatures typically range between 50 and 100 K, whereas dust temperatures are ~10 K. The properties of dense clouds have been deduced most effectively from radio telescope maps of a few molecular transitions. The temperatures and gas densities in the envelopes of these clouds are typically 5-10 K and 103-104 H2 molecules cm-3, respectively; however, in the core of clouds temperatures of at least 100 K and densities greater than 106 H2 molecules cm-3 are often observed or estimated. Finer spatial resolution in the radio-astronomy studies, where available, would likely reveal even hotter, denser gases. It is these core regions that are believed to be the sites of current star and planetary formation (Black et al., 1985). Since the 1970s, the presence of nearly 120 substances has been detected within these large dust and gas concentrates. With the recent detection of the first phosphorus-containing molecule (viz., PN) in an interstellar cloud, all the major constituents of life in the interstellar molecular inventory have now been demonstrated. Most of these constituents are organic compounds, and some are 64 rather complex molecules consisting of more than ten carbon atoms (se