Na⁺, F^–, Br^–, and Cl^– Adsorptions and Penetrations on an Ice Surface

Abstract

With the help of our quantum mechanical/effective fragment potential (QM/EFP) scheme, the adsorptions of Na + , F − , Br − , and Cl − ions on a hexagonal ice (0001) surface were theoretically studied. Drastically different adsorption behaviors depending upon ion signs and surface heterogeneity were observed. The positive Na + ion forms 4−5 Na + −O interfacial bondings, regardless of the number of hydrogen dangling bonds (HDBs), yielding consistent adsorptions with large stabilization energies from −49.2 to −65.6 kcal/mol. On the other hand, the binding strengths of negative ions are sensitive to the number of HDBs. In the particular binding sites where there is no HDB, both Cl − and Br − cannot form a stable surface adsorption product. At the same binding site, more reactive F − can undergo insertion reaction into surface hydrogen bonding. A molecular HF and a hydroxide are formed on a site with one HDB, showing that the surface acid−base chemistry may depend upon the surface heterogeneity. In general, the versatile bonding ability of Na + through s and empty p orbitals provides strong interactions with the ice surface by disrupting the surface hydrogen-bonding network, which, in turn, reduces its initial penetration barriers into the bulk. However, the ice surface structures are intact in the case of negative ion adsorptions, making their penetrations into the bulk difficult.

Reductive Adsorption of Atmospheric Oxidized Mercury on Ice: Insights from Density Functional Calculations

“…In another previous study, the B3LYP method was shown to usually underestimate the intermolecular interactions in the H 2 O molecular system (e.g., E B of H 2 O molecule) by ∼10% compared to the results of highly accurate CCSD­(T) or DMC calculations . Despite the differences in the methodology and the target system (with and without the Hg atom) between this and the previous study, both calculations show the strong interactions between halogens and the uppermost d­(H) atoms on ice surfaces, thereby demonstrating the feasibility of the adsorption behavior of Hg dihalides assessed in this study.…”

“…This role of ice will be mitigated under UV-C irradiation, which can release adsorbed halogens from ice and cause the direct photolysis of atmospheric Hg dihalides (e.g., HgBr 2 → HgBr + Br or Hg + 2Br; Table S2) 2 ; however, solar UV-C irradiation would be mostly absorbed by the ozone layer and hence have little influence. , Nevertheless, it should be further noted that the reactivity of the ice surface depends on the distribution of d­(H) atoms. In a recent theoretical study, the bonds with halogen ions (F – , Cl – , and Br – ) became stronger as the number of adjacent d­(H) atoms increased (i.e., depending on the proton order of the ice surface) . This result implies that the more the number of nearby d­(H) atoms, the stronger the adsorption strength of halogens.…”

“…A previous theoretical study employing the hybrid quantum mechanics and classical subsystems represented by the effective fragment potential (QM/EFP) method also revealed the strong adsorption of halogens on an ice surface with fully ordered d­(H) atoms (such as ice-Ih 1 ); E B (Cl – ) and E B (Br – ) were −2.2 and −2.1 eV/atom, respectively, while Cl – and Br – were bound to three nearby d­(H) atoms . In that study, the QM regions were calculated with B3LYP functional and 6-311++G­(d,p) basis sets based on DFT . In another previous study, the B3LYP method was shown to usually underestimate the intermolecular interactions in the H 2 O molecular system (e.g., E B of H 2 O molecule) by ∼10% compared to the results of highly accurate CCSD­(T) or DMC calculations .…”

“…The ice-Ih 2 surface was investigated to confirm the interaction between reactive hydroxyl radicals and atmospheric Hg and to compare with the results of ice-Ih 1 and ice-Ih 3 . While the exact ice surface structure is still elusive, the reactivity and adsorption affinity of the ice surface may vary widely depending on proton ordering. ,,, Thus, it may be desirable to model heterogeneous adsorption environments of ice surfaces with statistical distributions of hexagonal rings full of d­(H), those full of d­(O) (i.e., corresponding to ice-Ih 1 and ice-Ih 3 , respectively), and their intermediates having both d­(H) and d­(O). The effective electric field induced by the highly ordered d­(H) domain can affect the adsorption behavior of polar molecules on ice (see ref.…”

Atomistic View of Mercury Cycling in Polar Snowpacks: Probing the Role of Hg2+ Adsorption Using Ab Initio Calculations

“…To understand chemical processes in polar environments or interstellar media, unusual chemical reactions on ice-Ih surfaces have been studied with sophisticated experimental techniques [50,[77][78][79][80][81][82]. Theoretical approaches using the ab initio calculations have also been applied to the adsorption of specific adsorbents on ice-Ih surfaces, such as acids (HOCl, HCOOH, and CH 3 COOH), halide ions (F − , Cl − , and Br − ), alkali metals (Na and Na + ), and heavy metals (Hg 0 ) [19,49,83,84]. In these studies, the dangling H and O atoms and the proton defects were revealed to be the reactive adsorption sites on the (0001) cleaved surfaces because of their electronic instability.…”