Formation of c-C6H5CN ice using the SPACE TIGER experimental setup

TL;DR

This study demonstrates that benzonitrile can form in interstellar ice analogs through irradiation of benzene and nitrile mixtures, supporting its potential formation pathway in space environments.

Contribution

The paper introduces the SPACE TIGER experimental setup and provides laboratory evidence for benzonitrile formation via irradiation of benzene and nitrile ices, highlighting conditions relevant to interstellar chemistry.

Findings

Benzonitrile forms upon irradiation of benzene and nitrile ices at low temperatures.

Formation is quenched in water-rich ice matrices.

Formation occurs when benzene and nitrile are in CO-rich ice layers.

Abstract

Benzonitrile (c-C6H5CN) has been recently detected in cold and dense regions of the interstellar medium (ISM), where it has been used as a signpost of a rich aromatic organic chemistry that might lead to the production of polycyclic aromatic hydrocarbons (PAHs). One possible origin of this benzonitrile is interstellar ice chemistry involving benzene (c-C6H6) and nitrile molecules (organic molecules containing the -CN group). We have addressed the plausibility of this c-C6H5CN formation pathway through laboratory experiments using our new setup SPACE TIGER. The SPACE TIGER experimental setup is designed to explore the physics and chemistry of interstellar ice mantles using laser-based ice processing and product detection methods. We have found that c-C6H5CN is formed upon irradiation of c-C6H6$:CH3CN binary ice mixtures with 2 keV electrons and Lyman-alpha photons at low temperatures (4-10 K). Formation of c-C6H5CN was also observed when c-C6H6 and CH3CN were embedded in a CO ice matrix, but it was efficiently quenched in a H2O ice matrix. The results presented in this work imply that interstellar ice chemistry involving benzene and nitrile molecules could contribute to the formation of the observed benzonitrile only if these species are present on top of the ice mantles or embedded in the CO-rich ice layer, instead of being mixed into the H2O-rich ice layer.