Isomerization of hydrogen cyanide and hydrogen isocyanide in a cluster environment: quantum chemical study

Abstract

Hydrogen cyanide (HCN) and its isomer hydrogen isocyanide (HNC) are omnipresent in the interstellar medium (ISM). The ratio between the two isomers serves as an indicator of the physical conditions in different areas of the ISM. As such, the isomerization process between the two isomers has been extensively studied on the neutral potential energy surface. Moreover, HCN and HNC are thought to be precursors of important organic molecules, such as adenine. Here, we use quantum chemistry calculations and ab initio molecular dynamics simulations to focus on the chemistry that occurs upon ionization of pure HNC clusters. We demonstrate that upon ionization of HNC clusters, a distonic ion CN⋯HCNH+ is formed, and this formation is accompanied by HNC-to-HCN isomerization. Moreover, we show that the cluster environment and the network of hydrogen bonds are crucial for the isomerization process to occur and for the stabilization of the clusters. We demonstrate that, in contrast to HNC clusters, isomerization of ionized HCN clusters can occur only for the larger clusters. In addition, we discuss the formation of aminonitrile cation in the clusters and propose a barrierless route for diaminonitrile, a known precursor of amino acids and nucleobases, to form.

Singlet Oxygen Insertion into Hydrocarbons: The Role of First- and Second-Generation Pathways in Astronomically Relevant Ices

“…Here, we focus on reactions of hydrocarbons with oxygen in its singlet form, O( 1 D). A possible explanation for the difference in the products in the gas phase and the ice environment is that the molecules in the ice alter the potential energy surfaces (PES) as observed previously in the case of molecular clusters [25,26,50,51]. However, stability analysis of the different products on the PES reveals that while changes in stability were observed, they do not significantly alter the PES, as demonstrated in Appendix A.…”

“…Among the observed ices, water ice is the most abundant followed by carbon monoxide (CO) and carbon dioxide (CO 2 ), as well as smaller amounts of organic molecules such as methane (CH 4 ) and methanol (CH 3 OH) [23]. Gas-phase chemistry (including barrierless ion-molecule [24] and radical-molecule reactions) and gas-grain chemistry are possible pathways for the production of many of the observed species [8,[25][26][27][28]. The formation of different organic molecules in environments where temperatures are greater than 30 K can be explained via radical recombination mechanisms; the formation of radicals is followed by diffusion and recombination into larger molecular species [5,29,30].…”

NOx Reduction in a Cement Kiln with Spent Pot Lining: A Reaction Kinetics Study on HCN–NO and HNC–NO Interactions

“…In this study, we aim to understand and develop the complete reaction mechanism for the HCN reaction with NO to obtain N 2 and other byproducts. HCN and HNC conversion is the simplest isomerization process, and thereby, their interconversion has been studied by many researchers. − Here, we are specifically inclined toward studying NO reaction with both HCN and its tautomer, HNC, and in developing reaction pathways emerging from their interactions. Quantum chemistry calculations have been performed to obtain the possible intermediate species and the transition states.…”

In search of universalities in the dissociative photoionization of PANHs via isomerizations

“…HNC is known to be highly reactive and would rapidly isomerize to HCN under suitable conditions. [24][25][26] Its detection in the interstellar medium 27 in large quantities prompts the question of their production mechanism given its rapid isomerization to HCN in the presence of solid interfaces (grains, dust). Similarly, other astronomically relevant molecules, such as members of the cyanopolyyne family, have also been detected 19,28 as fragments from the dissociation of PANHs.…”