Quantum ionic dynamics in astrochemistry: Dipolar effects in theory and experiment

Negatively charged molecules have been observed in the interstellar medium a little more than ten years ago. Since the excess electron is usually bound with an energy amount that is smaller than that of the chemical bond between the atoms, the existence of a large amount of negative ions was not expected. The radioastronomical observations therefore led to several questions related to the formation and destruction of these interstellar anions. In this project we have investigated several important collision and reaction processes that can form or deplete negative ions. We have investigated reactions of hydrogen anions with neutral molecules that can form interstellar negative ions and compared the results to the process of radiative electron association. To gain more detailed understanding, we have studied the reverse process of near- threshold photodetachment and used the data to search for weakly-bound negative ion states that could serve as stepping stones for the formation of negative ions. Finally, we have investigated reactions of neutral hydrogen atoms with negative ions that forms neutral molecules and thereby destroy the anions. In summary we found that reactions of hydrogen anions may be at least as important for the formation of the observed interstellar anions as radiative electron attachment is. We also studied two anions that are similar to the observed anions, but have not been detected so far. For one of them we can rationalize this by low formation rates. For the other we calculate a formation rate that renders observation of this anion possible. The work in this project has been carried out by combining experiments on cold ions in radiofrequency traps with theoretical calculations of molecular potential curves and quantum scattering cross sections.