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Reaction of Nitrogen Dioxide with Ice Surface at Low Temperature (≤170 K)
Bang, Jaehyeock,Lee, Du Hyeong,Kim, Sun-Kyung,Kang, Heon American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.38
<P>We studied the adsorption and reaction of nitrogen dioxide gas on the surface of an ice film at temperatures of 100–170 K under ultrahigh vacuum (UHV) conditions. Cs<SUP>+</SUP> reactive ion scattering (RIS) and low-energy sputtering (LES) techniques were used to identify and quantify the reactants and products on the surface of the ice film, in conjunction with the use of temperature-programmed desorption (TPD) to monitor the species desorbed. Temperature-ramping experiments were performed to examine the changes in the populations of these species as a function of temperature. Adsorption of NO<SUB>2</SUB> gas on the ice film at <110 K produced physisorbed species that may possibly possess negative charge character (NO<SUB>2</SUB><SUP>δ-</SUP>), as deduced from the NO<SUB>2</SUB> and NO<SUB>2</SUB><SUP>–</SUP> signals in the RIS and LES experiments. At 110–130 K, NO<SUB>2</SUB><SUP>δ-</SUP> species were either desorbed as NO<SUB>2</SUB> gas or converted to nitrous acid (HONO), NO<SUB>3</SUB><SUP>–</SUP>, and H<SUB>3</SUB>O<SUP>+</SUP> on the surface. Nitrous acid gas was desorbed at 140–160 K. The efficiency of conversion of NO<SUB>2</SUB> to surface nitrous acid was about 40%, and that to nitrous acid gas was about 7%. The efficiency of the reaction of NO<SUB>2</SUB> on the ice surface may be higher than that at the gas/liquid water interface. The reaction efficiency increased with a decrease of the NO<SUB>2</SUB> coverage and was inversely correlated with the N<SUB>2</SUB>O<SUB>4</SUB> coverage, which favors the mechanistic interpretation that an isolated NO<SUB>2</SUB> molecule reacts with water. However, NO<SUB>2</SUB> can diffuse on the ice surface to form clusters at ≥120 K. Under these conditions, the possibility that dimerization of NO<SUB>2</SUB> contributes to the hydrolysis reaction of NO<SUB>2</SUB> may not be excluded.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-38/acs.jpcc.5b05497/production/images/medium/jp-2015-05497w_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b05497'>ACS Electronic Supporting Info</A></P>
Lee, Du Hyeong,Bang, Jaehyeock,Kang, Heon American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.22
<P>The charge at the surface of water and the resultant surface voltage play an important role in many natural phenomena and technological applications. However, the relationship between surface Charge and the interfacial distribution of H+ and OH- ions remains unclear. We measured the surface voltage produced by an ionized acid or a base at the surface of amorphous solid Water (ASW) using a Kelvin work-function probe and studied the depth distributions of H+ and OH- ions. H+ ions were distributed over a thicker region from the surface than OH- ions, although both ions reside preferentially at the surface. This difference led:to the formation of opposite surface charges in the presence of the acid or base. The deeper penetration of H+ ions is attributed to efficient proton transport, dynamics in the lattice and the resultant dynamic delocalization of protons. The study demonstrates that the asymmetric H+ and OH- distributions may be important to understand, the electrical and acid-base properties of ASW and crystalline ice surfaces and, possibly, those of the liquid water surface as well.</P>