Computer Simulation Investigation of the Adsorption of Cyanamide on Amorphous Ice at Low Temperatures

• Published in: Journal of physical chemistry. C 2020-05, Vol.124 (19), p.10615-10626
• Main Authors: Jedlovszky, Pál, Horváth, Réka A, Szőri, Milán
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c02075

The adsorption of cyanamide at the surface of low density amorphous (LDA) ice is studied by grand canonical Monte Carlo simulations in the temperature range of 50–200 K, under conditions characteristic of the interstellar medium and prebiotic Earth. The obtained results show that the adsorption is strictly monomolecular; moreover, condensation of cyanamide even precedes the saturation of the adsorption monolayer in the entire temperature range studied. Adsorbed cyanamide molecules are found to form altogether 3–4 hydrogen bonds with each other and with the surface water molecules at every surface concentration. As a consequence, their adsorption is strongly an exothermic process and hence becomes progressively more pronounced with decreasing temperature. Lateral H-bonding between the adsorbed cyanamide molecules leads to their noticeable clustering, evidenced also by the non-Langmuir character of the adsorption isotherm, becoming more pronounced at lower temperatures. Besides adsorption, cyanamide molecules are also found to be able to dissolve in the bulk LDA phase in a noticeable extent. However, contrary to the surface adsorption, dissolution turns out to be an entropy-driven, endothermic process and hence becomes more pronounced at higher rather than at lower temperatures.