Year: 2026
Type: article
Abstract: Hydrogen cyanide (HCN) is present in many astrochemical environments, including interstellar clouds and comets. On Saturn's moon Titan, large amounts of HCN ice are present in the atmosphere and, following surface deposition, may influence both chemical and geological evolution. However, despite HCN's relevance to origin of life chemistry, the physiochemical properties of its solid state remain poorly characterized. For example, the crystals of HCN exhibit a range of rare properties, including pyroelectricity, and the ability to glow and jump under certain conditions. Here we use quantum chemical methods to predict HCN crystal surface energies, from which we derive the needle-like, high-aspect-ratio morphology of HCN nanocrystals. The predicted tips expose high-energy polar facets imbued with strong electric fields. We suggest that the combination of tips of opposite polarity helps to explain the cobweb-structure of solid HCN, and that fracture can transiently expose energetic surfaces, capable of catalysis at low temperature. One such process is predicted to be the near-barrierless formation of isocyanide (HNC) on HCN crystals, following proton addition or abstraction, for example, via radiation or acid/base-chemistry. Such field-assisted surface mechanisms may contribute to HCN-to-HNC isomerization under relevant conditions, and are suggested to explain part of the out-of-equilibrium abundance of HNC in cold environments such as Titan's atmosphere, and, potentially, in cometary comae.
Source: ACS Central Science
Authors: Marco Cappelletti, Hilda Sandström, Martin Rahm
Institution: Chalmers University of Technology
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Funder: Vetenskapsrådet
OpenAlex ID: W7124149318