Penning Ionization by Collisions of Metastable Atoms with van der Waals Clusters

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First, penning ionizations of linear triatomic molecules (carbon dioxide, carbonyl sulfide, carbon disulfide, nitrous oxide), hexafluorobenzene, and pentafluorobenzene resulting from collisions of metastable helium atom(He^<**>) have been studied at 150 meV by combining the crossed-beam method with fluorescence spectroscopy. Emission cross sections for electronically excited parent ions and their vibrational distributions are determined and compared with the data obtaind by flowing afterglow and photoionization. The interactions between He^<**> and target molecules were examined on the basis of the dependences of emission cross sections upon the discharge power applied to the He^<**> beam source.Second, dissociative ionizations of CC1_4, CHC1_3, CFC1_3, CF_2C1_2, and CBrC1_3 by collisions of He^<**> are studied. Emission cross sections for several neutral fragments have been determined. Emission cross sections for these fragments are independent of the collision energy. This results prefers the harpoon mechanism.Papers concerning these results have been submitted to Chem. Phys. and J.Phys. Chem. More detailed studies of the collision-energy dependence of emission cross sections are being carried out in order to discuss more quantitatively the interaction potential between He^<**> and target molecules.