Effects of electric fields and collisions on highly excited rubidium atoms

Abstract.

The effects of static and pulsed electric fields on the multiphoton ionization (MPI) of rubidium atoms at both low (atomic beam) and high (heat pipe) densities are studied using tunable OPO lasers. Two-photon excitation of np states is induced by the external electric field at both low and high densities. In addition, np signal is also seen at very low electric fields in the heat pipe, providing evidence for collision mixing as well as field mixing. At low Rb densities strong resonance features are observed in the energy region between the zero field limit (IP) and the field ionization limit. In addition, collisional detachment and charge transfer between excited ns and nd Rb Rydberg states and nozzle-jet cooled polar molecules (acetonitrile and acetone) are studied under crossed-beam conditions. The formation of dipole bound anions for acetone is only seen under nozzle jet expansion conditions and the maximum in the Rydberg electron transfer (RET) rate versus n depends upon the expansion gas ($n_{\rm max}$ increases in the order H₂, He, Ne, Ar, Xe). For acetone (low dipole moment and large $n_{\rm max}$), collisional detachment dominates the charge transfer, whereas for acetonitrile (high dipole moment and low $n_{\rm max}$), charge transfer is seen to dominate the creation of Rb⁺.