Adsorption of cyanodiacetylene on ice: a periodic approach

The adsorption of cyanodiacetylene (HC5N) on ice has been investigated within a periodic approach at the density functional theory level using the parameter-free PBE0 hybrid functional. Two adsorption models, involving monodentate hydrogen bonding, have been considered. A third model, corresponding to a bridging binding model, has also been taken into account but found unstable. Calculations have been carried out considering two orientations of a proton-ordered model of ice surfaces, using two different unit cells in each case. Eight different cases of the adsorption of HC5N on ice have been investigated in depth at the geometric, energetic and electronic levels. Although HC5N is found to mainly bind to ice by direct hydrogen bonding, densities of states analysis suggest that its pi system plays a relevant role in the adsorption, especially by interaction with dangling surface hydrogen atoms, leading to significantly different adsorption geometries in all cases investigated. Analysis of the infrared spectral signature of HC5N shows the typical large red-shift of the H-C stretching mode frequency in the adsorption model involving hydrogen bonding between the H atom of HC5N and ice, in line with both experimental and previous theoretical findings based on cluster approaches.