Origin of Amino Acids and Organic Sugars in Interstellar Clouds

A theoretical model is outlined for the chemical manufacture of interstellar amino acids and sugars. Both organic molecules are formed inside the bulk interior of icy grain mantles photoprocessed by ultraviolet starlight. At first, ultraviolet photolysis creates a high concentration of free radicals in the mantles. Thereafter, the heat input from grain-grain collisions causes radicals to react chemically with one another and manufacture large organic molecules having a high molecular weight. Chemical explosions of processed mantles eject large fragments of organic dust into the ambient gaseous medium. The large fragments break up into smaller ones by sputtering and ultimately by photofission of individual molecules. A sizeable concentration of large organic molecules is still present in the gas phase as a consequence of balancing the molecule rate of supply from exploding grain mantles with the rate of molecule destruction. The model chemistry based on radical-radical reactions would explain the existence of both the amino acid glycine (NH₂CH₂COOH) and the sugar glycolaldehyde (CH₂OHCHO). Glycolaldehyde was recently detected in millimeter-wave rotational transition emission from the star-forming cloud Sagittarius B2.