A critical review of H3+ recombination studies

After more that 30 years of experimental and theoretical work it now appears that theory and experiment on H-3(+) recombination have finally converged. Since the storage ring results come very close to the latest theoretical calculations one might conclude that "the case is closed". However, some troublesome issues remain and should not be dismissed too quickly. For instance, some afterglow measurements showed faster decays at early afterglow times. It is now clear that the fast recombining species cannot be vibrationally excited ions since the same rates were found for spectroscopically identified H-3(+) ions in v=0. On the other hand, there is no convincing explanation for the very small rates obtained in the Prague experiments at low H-2 densities. It is also puzzling that some measurements find nearly the same recombination coefficients for H-3(+) and D-3(+), while others indicate that H-3(+) recombines much faster. It has often been stated that vibrational excitation of the H-3(+) ions tends to enhance recombination, but the evidence for that is far from solid; some observations suggest that the opposite is just as likely.