Role of atomic resonances in the ionization of potassium atoms in slow collisions with He(21,3S)

Cross sections have been calculated for the Penning ionization of ground-state potassium atoms in collisions with metastable He(2 ${}_{}{}^1{}_{}{}^{}$,3S) atoms for the range of center-of-mass-system energies 0.01 eV≤E≤1.0 eV. The cross sections were calculated using ab initio ptical potentials. The real part of the optical potential was obtained by adjusting the potential curve resulting from a configuration-interaction (CI) calculation performed on the HeK molecule so as to include the correct van der Waals asymptotic form. The imaginary part was obtained by performing a Stieltjes moment analysis of a discrete ($L^2$) representation of the ${\mathrm{HeK}}^{+}$+${\mathrm{e}}^{\mathrm{-}}$ continuum generated in a CI procedure. The calculated cross section for He(2 ${\mathrm{}}^3$S) scattered from K at E=0.032 eV is in good agreement with stationary afterglow measurements at room temperature. A nearly degenerate core-excited state of potassium [which has a curve crossing with the He(2 ${\mathrm{}}^3$S)K molecular state] is then explicitly included in a Landau-Zener formulation which further increases the calculated cross section, but it still agrees well with the room-temperature measurements. Elastic differential cross sections for He(2 ${\mathrm{}}^1$S) on K are also reported.