The nature of nitrate at the ice surface studied by XPS and NEXAFS

• Published in: Physical chemistry chemical physics : PCCP 2010-08, Vol.12 (31), p.887-888
• Main Authors: K epelová, Adéla, Newberg, John, Huthwelker, Thomas, Bluhm, Hendrik, Ammann, Markus
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Surface physical chemistry
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c0cp00359j

Trace contaminants such as strong acids have been suggested to affect the thickness of the quasi-liquid layer at the ice/air interface, which is at the heart of heterogeneous chemical reactions between snowpacks or cirrus clouds and the surrounding air. We used X-ray photoelectron spectroscopy (XPS) and electron yield near edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Advanced Light Source (ALS) to probe the ice surface in the presence of HNO 3 formed from the heterogeneous hydrolysis of NO 2 at 230 K. We studied the nature of the adsorbed species at the ice/vapor interfaces as well as the effect of HNO 3 on the hydrogen bonding environment at the ice surface. The NEXAFS spectrum of ice with adsorbed HNO 3 can be represented as linear combination of the clean ice and nitrate solution spectrum, thus indicating that in the presence of HNO 3 the ice surface consists of a mixture of clean ice and nitrate ions that are coordinated as in a concentrated solution at the same temperature but higher HNO 3 pressures. At submonolayer nitrate coverage, up to 20% of water near the ice surface is engaged in hydrating nitrate and 80% in crystalline ice.