The smallest drop of acid it is possible to make has been spotted within superfluid helium nanodrops cooled to below 1 kelvin.
Martina Havenith of Ruhr University Bochum in Germany and her colleagues observed the reaction between one molecule of hydrochloric acid and four of water using infrared laser spectroscopy. Using ab initio simulations, they found that the dissociation into H+ and Cl− occurs in a stepwise manner (pictured, right). A novel mechanism, which the authors term 'aggregation-induced dissociation', explains how this can happen even at such ultralow temperatures.
Such dissociations are key in chemistry, with relevance to processes ranging from reactions in polar clouds to spontaneous synthesis in space, the authors say.