Speaker
Description
Negative molecular ions have drawn a lot of attention in recent years, because of their detection in interstellar space and of opportunities to use laser-cooled anions to cool antiproton. Cryogenic radiofrequency ion traps are well suited tools to study the quantum states and state-selected chemistry of negative ions. Using photodetachment spectroscopy we have probed rotational quantum states of cold trapped anions and studied rotational state-changing collisions at low temperature. This also allowed us to perform rotational terahertz spectroscopy and infrared overtone spectroscopy. We have further studied photodetachment of two interstellar anions near threshold. For CN- the measurements are well described by Wigner's threshold law. For C3N- the large permanent dipole moment of C3N leads to a qualitatively different cross section behavior. Furthermore, the rotational contour of a dipole bound state was resolved slightly below the detachment threshold in agreement with calculations. This state could serve as a doorway state to negative ion formation in interstellar clouds. Recently, we have developed a two-photon scheme to probe rotational and vibrational states of the homonuclear anion C2-, a candidate proposed for negative ion laser cooling. Results on electronic spectroscopy and vibrational relaxation collisions of this ion will be presented.
