Acid-base chemistry on crystalline ice: HCl+NH3

The chemical interaction of (i) HCl (ii) NH3, and (iii) HCl + NH3 with crys talline ice has been examined as a function of temperature (T = 80-150 K) u tilizing FTIR spectroscopy. The infrared spectra reveal the formation of io nic hydrates for HCl and molecular hydrates for NH3. The acid-base reaction leads to the formation of the ammonium ion, NH4+. While it is produced to a limited extent between 80 and 140 K, NH4+ is a dominant species above 140 K. All species appear as lower amorphous hydrates for T = 80-140 K. Dramat ic changes in the spectra occur above 140 K as higher crystalline hydrates are formed. This temperature coincides with the amorphous to crystalline ph ase transformation of ice. This change appears to be due to a greater numbe r of water molecules on the surface that are available for hydration and cr ystallization.