Abstract. The partitioning of nitrogen oxides between ice and air is important to the ozone budget in the upper troposphere. In the present study, the adsorption of nitrogen oxides on ice was investigated at atmospheric pressure using a chromatographic technique with low concentrations of radioactively labelled nitrogen oxides. The measured retentions solely depended on molecular adsorption and were not influenced by dimerisation, formation of encapsulated hydrates on the ice surface, dissociation of the acids, nor by migration into a quasi-liquid layer or grain boundaries. Based on the chromatographic retention and the model of thermochromatography, the adsorption enthalpies of −20 kJ mol −1 for NO, −22 kJ mol −1 for NO 2 , −30 kJ mol −1 for peroxyacetyl nitrate, −32 kJ mol −1 for HONO and −44 kJ mol −1 for HNO 3 were calculated. To assess the adsorption enthalpies, standard adsorption entropies were calculated based on statistical thermodynamics. In this work, the use of two different standard states was demonstrated. Consequently different values of the standard adsorption entropy, of either between −39 J (K mol) −1 and −45 J (K mol) −1 , or −164 J (K mol) −1 and −169 J (K mol) −1 for each nitrogen oxide were deduced. The adsorption enthalpy derived from the measurements, was independent of the choice of standard state. A brief outlook on environmental implications of our findings indicates that adsorption on ice might be an important removal process of HNO 3 . In addition, it might be of some importance for HONO and peroxyacetyl nitrate and irrelevant for NO and NO 2 .

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Structure and electronic properties of one-dimensional bimetallic In-Sn chains formed by codeposition on a Si(100)-2×1 surface are studied experimentally by means of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy and theoretically using density-functional theory. The codeposition of In with a small amount of Sn allows separation of various In-Sn structures and their identification in empty-state STM images. A 16 × 2 supercell is employed to model an indium atomic chain in which one or two Sn atoms are embedded. This atomic model is used to identify unambiguously various In-Sn structures observed experimentally. At low Sn:In ratio the codeposition results in strongly preferential formation of isolated heterogeneous In-Sn dimers. The In-Sn dimer induces tilting of the neighboring homogeneous In-In dimer accompanied with a charge transfer. Consequently a localized state at Fermi level appears. These results contribute to a discussion on possible transport of electric charge along one-dimensional atomic chains of metals.

Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert. Furthermore, the reactivity of the Sn terminated surface is found to be considerably decreased in comparison with Si(001)2 × 1. According to the proposed adsorption model ethylene bonds to Sn dimers via [2 + 2] cycloaddition by interacting with their π dimer bonds. In contrast, indium dimers do not contain π bonds, which renders the In terminated Si(001) surface inert for ethylene adsorption.

Abstract. The partitioning of nitrogen oxides between ice and air is of importance to the ozone budget in the upper troposphere. In the present study, adsorption of nitrogen oxides on ice was investigated at atmospheric pressure using a chromatographic technique with radioactively labelled nitrogen oxides at low concentrations. The measured retentions solely depended on molecular adsorption and were not influenced by dimerisation, formation of encapsulated hydrates on the ice surface, dissociation of the acids, nor by migration into a quasi-liquid layer or grain boundaries. Based on the chromatographic retention and the model of thermo-chromatography, the standard adsorption enthalpy of -20 kJ mol-1 for NO, -22kJ mol-1 for NO2, -30kJ mol-1 for peroxyacetyl nitrate, -32kJ mol-1 for HON} and -44 kJ mol-1 for HNO3 was calculated. To perform those calculations within the model of thermo-chromatography, the standard adsorption entropy was calculated based on statistical thermodynamics. In this work, two different choices of standard states were applied, and consequently different values of the standard adsorption entropy, of either between -39 kJ mol-1 and -45kJ mol-1, or -164 kJ mol-1 and -169 kJ mol-1 for each nitrogen oxide were derived. The standard adsorption enthalpy was identical for both standard adsorption entropies and thus shown to be independent of the choice of standard state. A brief outlook on environmental implications of our findings indicates that adsorption on ice might be an important removal process of HNO3. In addition, it might be of some importance for HONO and peroxyacetyl nitrate and irrelevant for NO and NO2.