Mechanism for the destruction of H3+ ions by electron impact

The rate at which the simplest triatomic ion (H3+) dissociates following recombination with a low-energy electron has been measured in numerous experiments1,2,3,4,5,6,7,8,9,10. This process is particularly important for understanding observations of H3+ in diffuse interstellar clouds11,12,13. But, despite extensive efforts14,15, no theoretical treatment has yet proved capable of predicting the measured dissociative recombination rates at low energy, even to within an order of magnitude. Here we show that the Jahn–Teller symmetry-distortion effect16,17,18,19—almost universally neglected in the theoretical description of electron–molecule collisions—generates recombination at a much faster rate than any other known mechanism. Our estimated rate constant overlaps the range of values spanned by experiments. We treat the low-energy collision process as a curve-crossing problem, which was previously thought inapplicable20 to low-energy recombination in H3+. Our calculation reproduces the measured propensity for three-body versus two-body breakup of the neutral fragments3, as well as the vibrational distribution4 of the H2 product molecules.