Complex Molecules and the GBT: Is Isomerism the Key?

Abstract

Interstellar aldehydes have been called the “sugars of space” ever since the discoveries of formaldehyde (H2CO) in 1969 and acetaldehyde (CH3CHO) in 1973. At present, more than 135 interstellar molecular species have been identified. Excluding diatomic species, 30% of all interstellar molecules have isomeric counterparts. The newest instrument in the interstellar molecule search arsenal is the Green Bank Telescope (GBT), which is credited with the discovery of the large aldehydes propenal (CH2CHCHO) and propanal (CH3CH<2CHO). In addition, the GBT has been used to observe interstellar glycolaldehyde (CH2OHCHO), the simplest possible aldehyde sugar, and interstellar ethylene glycol (HOCH2CH2OH), the sugar alcohol of glycolaldehyde. These new GBT observations that suggest a universal prebiotic chemistry are presented and discussed. While there is no consensus regarding how large complex interstellar molecules are formed, it may be that the first step in the polymerization of interstellar formaldehyde (H2CO) with its isomer trans hydroxy methylene (t-HCOH) is responsible for the formation of interstellar glycolaldehyde. We discuss this polymerization mechanism that can result in the generation of more complex sugars. We assess the likelihood of interstellar trans hydroxy methylene and suggest a search strategy for it using the GBT.