Scientists in Germany have observed a single molecule of HCl dissociating into its component ions in water - and have discovered that just four water molecules are needed for complete dissociation of the acid. The team say that their findings, made under ultracold conditions, should help scientists understand nanoscale chemical transformations at very low temperatures, including those occurring in stratospheric clouds and interstellar media. Previous studies into the dissociation mechanism of the strong acid HCl at ultracold temperatures had left a puzzle. Normally, such reactions require thermal energy, but at ultracold temperatures this thermal energy is not available. Now, Martina Havenith and...