Vacuum ultraviolet photodissociation and surface morphology change of water ice films dosed with hydrogen chloride

Abstract

Time-of-flight (TOF) spectra of photofragment H atoms from the photodissociation of water ice films at 193 nm were measured for amorphous and polycrystalline water ice films with and without dosing of hydrogen chloride at 100-145 K. The TOF spectrum is sensitive to the surface morphology of the water ice film because the origin of the H atom is the photodissociation of dimerlike water molecules attached to the ice film surfaces. Adsorption of HCl on a polycrystalline ice film was found to induce formation of disorder regions on the ice film surface at 100-140 K, while the microstructure of the ice surface stayed of polycrystalline at 145 K with adsorption of HCl. The TOF spectra of photofragment Cl atoms from the 157 nm photodissociation of neutral HCl adsorbed on water ice films at 100-140 K were measured. These results suggest partial dissolution of HCl on the ice film surface at 100-140 K.

Classical and quantum studies of the photodissociation of a HX (X=Cl,F) molecule adsorbed on ice

“…It is well known that in water, HCl shows complete ionic dissociation ͑strong acid͒, while HF presents partial ionization ͑weak acid͒. 14 From a theoretical point of view, UV irradiation of adsorbed molecules producing radicals at/in the ice surface is still poorly understood. 7,[9][10][11] More generally, up to now, very few studies have been dedicated to photolytic processes occurring at the ice surface.…”

Emergence of Charge-Transfer-to-Solvent Band in the Absorption Spectra of Hydrogen Halides on Ice Nanoparticles: Spectroscopic Evidence for Acidic Dissociation

“…At very low temperatures, HCl stays intact on the ice surface, whereas with increasing temperature, it starts to dissociate. For isolated hydrogen halides on ice surfaces, the transition between an intact and dissociated form probably takes place between 80 and 120 K. The process of HX dissociation on ice was studied using infrared spectroscopy, – reactive ion scattering, , X-ray absorption spectroscopy, various other surface analysis methods, and most recently H-photofragment time-of flight spectrometry . The structure of the ice surface doped with HCl or HBr has also been addressed theoretically. ,, …”