Interstellar Chemical Evolution: Probing HCN and HNC Formation and Destruction on Icy Surfaces with Computational Chemistry

HCN and HNC are routinely used by astronomers to trace temperature and dense gas regions in galaxies, where stars and planetary systems form. They are key precursors of complex species, including prebiotic molecules like amino acids and nucleotides.

While their gas-phase formation and evolution are well understood, their formation and destruction paths on interstellar ices remains largely unchartered territory.The aim of this proposal is to remedy this knowledge gap by investigating the formation of HCN and HNC through CN radical hydrogenation on interstellar water and CO ices, as well as their destruction paths using state-of-the-art computational chemistry and astrochemical modelling.

Including, in all cases, their deuterated counterparts.

It also presents an opportunity to study the interaction of CN radicals with ice surfaces, which can occur either through physisorption or hemibonding on both types of ices.

The four primary objectives of this proposal are: (i) to explore the CN to water and CO ice binding energy distribution as well as the dominant binding modes, (ii) to quantify the hydrogenation reactions of CN with atomic and molecular hydrogen forming HCN and HNC, as well as other possible hydrogenation products due to the hemibonding interactions, (iii) to investigate the destruction of the products in the previous point resulting from further hydrogenation reactions, and finally, (iv) to calculate the rate constants, including quantum tunnelling, and implement these in the UCLCHEM astrochemical model to assess the importance of surface chemistry in two specific cases: the shocked region L1157-B1 and the NGC1068 galaxy.The novelty of this proposal lies in the combination of computational chemistry and astrochemical modelling to unveil the ice-surface formation and evolution of HCN and HNC and their deuterated counterparts for the first time, encompassing a comprehensive characterization of the CN to water and CO hemibonding interaction.