H3+ Between the Stars

The presence of H3+ in the interstellar medium was forecast almost four decades ago. Almost three decades ago it was asserted that its reactions with neutral molecular and atomic species directly lead to the production of many of the interstellar molecules that have been discovered by radio and infrared astronomers. With the recent detection of H3+ in interstellar space, astronomers finally have direct confirmation of H3+ as the foundation of ion-molecule interstellar chemistry. Although many questions remain to be answered, it is clear that H3+is a unique tool for understanding the properties of interstellar clouds.