New insights into the formation of interstellar formamide , a species of great relevance in prebiotic chemistry , are provided by electronic structure and kinetic calculations for the reaction NH _ { 2 } + H _ { 2 } CO \rightarrow NH _ { 2 } CHO + H. Contrarily to what previously suggested , this reaction is essentially barrierless and can , therefore , occur under the low temperature conditions of intestellar objects thus providing a facile formation route of formamide .
The rate coefficient parameters for the reaction channel leading to NH _ { 2 } CHO + H have been calculated to be A = 2.6 \times 10 ^ { -12 } cm ^ { 3 } s ^ { -1 } , \beta = -2.1 and \gamma = 26.9 K in the range of temperatures 10-300 K. Including these new kinetic data in a refined astrochemical model , we show that the proposed mechanism can well reproduce the abundances of formamide observed in two very different interstellar objects : the cold envelope of the Sun-like protostar IRAS16293-2422 and the molecular shock L1157-B2 .
Therefore , the major conclusion of this Letter is that there is no need to invoke grain-surface chemistry to explain the presence of formamide provided that its precursors , NH _ { 2 } and H _ { 2 } CO , are available in the gas-phase .