Rate coefficients for the reactions of ions with polar molecules at interstellar temperatures

A theory has been developed recently which predicts that the rate coefficients, k, for the reactions of ions with polar molecules at low temperatures will be much greater than the canonical value of 10-9 cm3 s-1. The new theory indicates that k is greatest for low-lying rotational sates and increases rapidly with decreasing temperature. We refer to recent laboratory measurements which validate the theory, present calculated values of k for the reactions of H+3 ions with several polar molecules, and discuss their significance to interstellar chemistry. For the reactions of ions with molecules having large dipole moments, we recommend that k values as large as 10-7 cm3 s-1 should be used in ion-chemical models of low-temperature interstellar clouds