Probing the interaction of hydrogen chloride with low-temperature water ice surfaces using thermal and electron-stimulated desorption

摘要

The interaction and autoionization of HCl on low-temperature (80-140 K) water ice surfaces has been studied using low-energy (5-250 eV) electron-stimulated desorption (ESD) and temperature programmed desorption (TPD).There is a reduction of H~+ and H_2~+] and a concomitant increase in H~+(H_2O)_(n=1-7) ESD yields due to the presence of submonolayer quantities of HCl. These changes are consistent with HCl induced reduction of dangling bonds required for H ~+ and H_2~+] ESD and increased hole localization necessary for H~+(H_2O)_(n=1-7 ESD). For low coverages, this can involve nonactivated autoionization of HCl, even at temperatures as low as 80 K; well below those typical of polar stratospheric cloud particles. The uptake and autoionization ofHCl is supported by TPD studies which show that for HCl doses ≤0.5±0.2ML (ML =monolayer) at 110K, desorption of HCl begins at 115 K and peaks at 180 K. The former is associated with adsorption of a small amount of molecular HCl and is strongly dependent on the annealing history of the ice. The latter peak at 180 K is commensurate with desorption of HCl via recombinative desorption of solvated separated ion pairs. The activation energy for second-order desorption of HCl initially in the ionized state is 43±2 kJ/mol. This is close to the zero-order activation energy for ice desorption.