Optical model calculation of the total Penning ionization cross sections for He(2 1P)–Ar, Kr, and Xe

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Abstract
Quantum mechanical calculation of the total Penning ionization cross sections for He(2 1P) –Ar, Kr, and Xe collisions has been made in the region of the collisional energy from 0.1 meV to 1 eV with an optical complex potential approach for an electronic transition. The real part of an optical potential at long range is expressed in an explicit dispersion form and that in a repulsive region is expressed in a shielded Coulomb form. We have determined a repulsive potential by an excellent fit with our experimental cross sections. The imaginary part of the optical potential at long range is expressed by a dipole–dipole autoionization width, and at a small interatomic distance an electron exchange width is also considered to account an exponentially dispersive increase of the autoionization width. Good agreement between the present calculation and the experimental data has been obtained both in the energy dependence and in the absolute cross section values. The real part of the optical potential for He(2 1P) –Ar, Kr, or Xe is analogous to that for He(2 1S) –Ar, Kr, or Xe, respectively. It has been found that the width for the electron exchange effectively increases the total Penning ionization cross section, particularly in the case of He(2 1P) –Xe.