Theoretical interstellar and prebiotic organic chemistry: a tentative methodology.

A theoretical methodology for the systematic study of the interstellar molecules is proposed. Some examples, dealing with formaldehyde excited states, formyl radical and ion, reactivity of the excited states of formic acid, methyl cyanide and methyl acetylene, as well as the reaction patho of formaldehyde photodecomposition are presented. Quantum chemical methods appear to be a powerful tool to study the structure and behaviour of molecules related with interstellar space and the Origin of Life.