Reflection–absorption IR spectroscopic investigation of the photolysis of thin films of dichlorine monoxide and chlorine dioxide

Abstract

Reflection–absorption infrared (RAIR) spectroscopy and mass spectrometry have been employed in order to investigate the low-temperature photochemistry of thin films of chlorine dioxide, OClO, and dichlorine monoxide, Cl ₂ O, grown on a gold foil in an ultra-high vacuum system. Photolysis of a neat film of OClO (λ>300 nm, 90–110 K) produces chloryl chloride, ClClO ₂ . Irradiation of a co-deposited OClO/H ₂ O film also produces chlorine superoxide, ClOO, which suggests that OClO isomerisation is the first step in the reaction producing ClClO ₂ . Photolysis of Cl ₂ O (300<λ<515 nm, 90–110 K) is shown to produce OClO, initially, which is subsequently converted to ClClO ₂ . Analysis of the observed IR band intensities and consideration of the metal surface selection (MSS) rule indicates that the photochemically produced OClO intermediate aligns perpendicular to the gold substrate. Mechanistic details and the atmospheric implications of the chemistry are discussed.