Experimental and theoretical study of the Penning ionisation of H atoms by He metastables

The Penning ionisation systems He(2 3 S)/H and He(2 1 S)/H have been studied experimentally in the thermal range of relative collision energies. The authors report results for the energy distribution of the ejected electrons, total ionisation cross sections and associative to total ionisation cross section ratios. By reproducing these experimental data for He(2 3 S)/H in quantum-mechanical model calculations, the authors were able to derive an accurate complex potential for this system and to confirm the approximate validity of the theory used. The potential so determined is used to calculate measurable quantities, which are then compared with other available experimental data. The limitation of the theory, which becomes evident in the calculations, is discussed.