Rydberg molecules, electron collisions, and associative ionization

真司 植松

Byron George Zollars

A. Kalamarides, C. W. Walter, Byron George Zollars +2 more

Measurements of associative ionization in collisions of K(nd) Rydberg atoms with a variety of molecular targets are reported, demonstrating that the Rydberg electron can serve as a catalyst to promote reactions involving the Rydberg core ion.

F. B. Dunning, R. F. Stebbings

Raymond Flannery, Valentin N. Ostrovsky, N. V. Prudov +1 more

A. Pesnelle, C. Ronge, M. Perdrix +1 more

The ionization of He atoms, prepared in a well-defined (n=14) $^{1}$P Rydberg state, in collisions with electron-attaching molecules like ${\mathrm{SF}}_{6}$ and ${\mathrm{NO}}_{2}$, is studied in a crossed-beam experiment at thermal energies. The ionization cross section is observed to be large for ${\mathrm{SF}}_{6}$, reaching 4.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ ${\mathrm{cm}}^{2}$, and to be smaller for ${\mathrm{NO}}_{2}$, close to ${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$. The dependence of these two cross sections on the relative velocity of the reactants exhibits a characteristic behavior with a saturation at low velocities, a dependence that is completely different from that obtained with polar molecules. The observation of such a dependence for ${\mathrm{NO}}_{2}$ indicates that, for this molecule, the reaction product is an ion pair, as for ${\mathrm{SF}}_{6}$, and that ionization is not due to rotational energy transfer even though ${\mathrm{NO}}_{2}$ has a dipole moment. This dependence cannot be explained by the ``free-electron model'' usually used in Rydberg-atom--molecule collisions; it clearly shows that the interaction of the molecule with the ion core cannot be neglected.