Adsorption Energies of Carbon, Nitrogen, and Oxygen Atoms on the Low-temperature Amorphous Water Ice: A Systematic Estimation from Quantum Chemistry Calculations

Abstract

We propose a new simple computational model to estimate adsorption energies of atoms and molecules to low-temperature amorphous water ice, and we present the adsorption energies of carbon ( 3 P), nitrogen ( 4 S ), and oxygen ( 3 P) atoms based on quantum chemistry calculations. The adsorption energies were estimated to be 14100 ± 420 K for carbon, 400 ± 30 K for nitrogen, and 1440 ± 160 K for oxygen. The adsorption energy of oxygen is well consistent with experimentally reported value. We found that the binding of a nitrogen atom is purely physisorption, while that of a carbon atom is chemisorption in which a chemical bond to an O atom of a water molecule is formed. That of an oxygen atom has a dual character both physisorption and chemisorption. The chemisorption of atomic carbon also implies a possibility of further chemical reactions to produce molecules bearing a C-O bond, while it may hinder the formation of methane on water ice via sequential hydrogenation of carbon atoms. These would be of a large impact to the chemical evolution of carbon species in interstellar environments. We also investigated effects of the newly calculated adsorption energies onto chemical compositions of cold dense molecular clouds with the aid of gas-ice astrochemical simulations. We found that abundances of major nitrogen-bearing molecules, such as N 2 and NH 3 , are significantly altered by applying the calculated adsorption energy, because nitrogen atoms can thermally diffuse on surfaces even at 10 K.

Neural-network assisted study of nitrogen atom dynamics on amorphous solid water – I. adsorption and desorption

“…It implies a broad distribution of binding sites as expected for an amorphous surface. Note that our results for the binding energy are in excellent agreement with those presented by Shimonishi et al (2018), who report an average value of 400 K, and close to the experimental value found by Minissale, M. et al (2016), differing only by a factor of about 2. It is important to keep in mind that the distribution of binding energies is broad, implying that the factor is only an averaged value.…”

“…With this work, we have provided data on sticking and desorption. Our values for the binding energies are in very close agreement with the ones obtained in Shimonishi et al (2018) and in good agreement with the experimental results of Minissale, M. et al (2016) (by a factor of 1.8). The dispersion in our results is significant, indicating that the low binding energy of nitrogen is strongly dependent on the adsorption sites.…”

“…Nitrogen interstellar chemistry is deeply affected by physical processes before chemical reactions. As it was studied by Shimonishi et al (2018), binding energies significantly affect the chemistry of nitrogen in molecular clouds. Combining ab-initio and rate equation approaches, they recalculated the N-ASW adsorption energies and N-bearing molecular abundances.…”

New insights into decomposition characteristics of nanoscale methane hydrate below the ice point

“…Water molecules of the ASW structure were described by the TIP3P force eld. [34][35][36] The O-H bond length of water molecules was set at 0.096 nm and the H-O-H bond angle was set at 104.52 . The non-bond effect of van der Waals between molecules was calculated using a Lennard-Jones potential energy function.…”

Gas Sensing Properties of Cobalt Titanate with Multiscale Pore Structure: Experiment and Simulation

“…, N) denotes the number of time increment. The adsorption energy E abs was estimated to be in the range of 10-20 kJ/mol [46]. The following dimensionless variables were introduced for normalizing the governing equation:…”