Gas phase formation of the prebiotic molecule formamide: insights from new quantum computations

TL;DR

This study demonstrates that formamide can form in interstellar space through a barrierless gas-phase reaction between NH2 and H2CO, challenging previous assumptions about its formation requiring grain-surface chemistry.

Contribution

The paper provides new quantum calculations showing the reaction NH2 + H2CO to form NH2CHO is barrierless and offers updated kinetic parameters, supporting gas-phase formation of formamide in space.

Findings

Reaction is essentially barrierless at low temperatures.

Refined astrochemical models match observed formamide abundances.

Gas-phase formation suffices without grain-surface chemistry.

Abstract

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 NH2 + H2CO -> NH2CHO + H. Contrarily to what previously suggested, this reaction is essentially barrierless and can, therefore, occur under the low temperature conditions of interstellar objects thus providing a facile formation route of formamide. The rate coefficient parameters for the reaction channel leading to NH2CHO + H have been calculated to be A = 2.6x10^{-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, NH2 and H2CO, are available in the gas-phase.