Low Temperature Surface Formation of NH3 and HNCO: hydrogenation of nitrogen atoms in CO-rich interstellar ice analogues

TL;DR

This study experimentally investigates how NH3 and HNCO form on icy interstellar grains at low temperatures, revealing new pathways for nitrogen chemistry relevant to astrochemistry and astrobiology.

Contribution

It provides the first laboratory evidence of solid HNCO formation via surface reactions in CO-rich interstellar ice analogues, highlighting a new formation route.

Findings

Solid HNCO forms through CO and NH radicals interaction.

NH3 and HNCO formation occurs at astrochemically relevant temperatures.

Reveals new surface reaction pathways for nitrogen species in space.

Abstract

Solid state astrochemical reaction pathways have the potential to link the formation of small nitrogen-bearing species, like NH3 and HNCO, and prebiotic molecules, specifically amino acids. To date, the chemical origin of such small nitrogen containing species is still not well understood, despite the fact that ammonia is an abundant constituent of interstellar ices toward young stellar objects and quiescent molecular clouds. This is mainly because of the lack of dedicated laboratory studies. The aim of the present work is to experimentally investigate the formation routes of NH3 and HNCO through non-energetic surface reactions in interstellar ice analogues under fully controlled laboratory conditions and at astrochemically relevant temperatures. This study focuses on the formation of NH3 and HNCO in CO-rich (non-polar) interstellar ices that simulate the CO freeze-out stage in dark interstellar cloud regions, well before thermal and energetic processing start to become relevant. We demonstrate and discuss the surface formation of solid HNCO through the interaction of CO molecules with NH radicals - one of the intermediates in the formation of solid NH3 upon sequential hydrogenation of N atoms. The importance of HNCO for astrobiology is discussed.