Velocity dependence of the penning ionization cross section of D atoms by He (2 1S) and He (2 3S) atoms

Associative ionization in collisions of with and

“…In conclusion, we believe that the similarity of the cross sections observed for reactions (11) and ( 16) is purely accidental, the two reactions actually proceeding along Relative velocity (10 6 cms σ ( 10 cm )…”

“…There is no theoretical prediction with which our results could be directly compared but there are data, both experimental and theoretical, on a related process: associative ionization in the collision of the neutral species H or D and He (n = 2) [7][8][9][10][11]13]. In figure 4 we show, together with our results, the cross sections for associative ionization of H or D with He(2 3 S)…”

“…For most of the points, it was about 10% (90% confidence level). In tables 3 and 4 we present the results of the measurement of the absolute cross sections for reactions (10) and (11). In figure 2 we show the two cross sections as a function of the barycentric energy E cm .…”

“…It is also clear that the 2 3 S cannot dominate the associative ionization. If it did, the cross section for reaction (11) at energy E would have to be of the same order as that of reaction (16) at energy E + 4 eV, because of the kinetic energy gained (4 eV) by the ionic reactants before reaching the crossing at 7a 0 ; this is obviously not the case. The rate of associative ionization is determined by the electron-electron interaction and by the nuclear matrix elements coupling the bound states with the vibrational continuum.…”

“…The collision of metastable He with H and D leading to the same products as ( 1) and (4) has also been investigated both experimentally and theoretically by Howard et al [7], Neynaber et al [9,12], Hickman et al [10], Magnuson et al [8], Fort et al [11] and Waibel et al [13].…”