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We have observed the process of associative ionization (AI) in collisions between hydrogen and rare gas atoms both prepared in their ground states (H + XXH+ + e- with X = Ar,Kr,Xe). This is the first experimental observation of this process, which we compare to the other charge-producing cross sections reported previously. AI takes place only in a small region of collision energies close to threshold. The cross sections show a distinct maximum, with a typical value of about 2×10-19 cm2. In contrast to the heavier rare gases AI is not observed in collisions of atomic hydrogen with He and Ne.

Absolute single-particle detection efficiencies of a microchannel plate (MCP) detector were determined by photo-ionization of atoms or molecules. The ionized heavy particles were detected in coincidence with the resulting electrons. This method allows the determination of detection efficiencies without a knowledge of the absolute event rates. We obtained the detection efficiencies for the ions H2+, D2+, HD+, H+, D+ and Ar+ in the impact energy range 0-5 keV. The detection efficiencies saturate above 3 keV and reach generally 41%. This value seems to reflect mainly the physically effective area of the MCP.

We report integral cross sections for the collision processes between H(D) atoms and H2(D2) molecules in the energy range from threshold to 170 eV leading to charged collision products. We observe not only charge exchange and target or projectile ionization such as H+H2 to H-+H2+ and H+H2 to H+e+H2+ but also associative ionization, H+H2 to H3++e, and heavy particle exchange, D+H2 to HD++H-. Typical absolute cross section values are between 10-21 cm2 and 10-17 cm2.

For the molecules CO, N 2 and O 2 the cross sections for the electron impact triple and quadruple ionization have been measured from threshold up to an electron energy of 1 keV. The cross sections are compared with the total electron impact ionization cross section. For the triply ionized molecules the initial kinetic energy of the fragment ions is measured and appearance energies are determined.

The fragmentation of CF4+ ( X 2T1), CF4+( A 2T2), N2O+( A 2Σ+) and COS+ ( A 2Π) all involve the release of large kinetic energies. Details of these and other fragmentations studied by the coincidence method are reported and discussed in relation to other experimental findings. The kinetic energy release in formation of CF3+ from CF4+ ( X 2T1) sets a new upper limit of 14.84±0.05 eV on the dissociation asymptote. A new metastable in the electron impact mass spectrum of COS, predicted from a previous coincidence result, is also reported.

The 21.22-eV photoelectron spectrum has been measured from a barium beam. Aside from the ground state of Ba + , the first six excited states of this ion have been identified. An unusually high relative cross section for the production of Ba 2+ and excited Ba + compared to Ba + in its ground state is found. An explanation is proposed involving the autoionizing (5p) 5 (6s) 2 2 P 1/2 state of Ba + . From this the binding energy of the 5P 1/2 electrons of Ba is found to be 21.1 eV.

Detailed integral cross sections of processes H + M → H−, H+ + e + M, H + e + M+ (M  Ne,Ar,Kr,Xe,O2) are reported in the low energy region (E < 100 eV or E < 500 eV for M+ + e). In general, ion pair formation is the dominating process at low energy and has a stongly oscillating cross section; free electron cross sections are monotonously rising.

The decay of doubly-charged molecular ions, produced by electron impact is investigated by a new method. The singly-charged decay products and their kinetic energy distributions are measured in coincidence as a function of the energy of the ionizing electrons up to 1000 eV. Results for H2, N2, O2, CO and NO are presented.

The energy dependence of the photoelectron angular distribution of mercury was measured in the region below the first excited state of the ion. The asymmetry parameter β shows remarkable deviations from β = 2 and a sharp resonant structure with β down to zero.

The branching ratio between the two components of the 62P state of Barium ions, produced by photoionization with Hel light (21.22 eV) from a discharge source, can be changed by a factor of two or more by changing the He discharge conditions.

The energy dependence of the photoelectron angular distribution of zinc was measured from 11.1 to 12.4 eV photon energy. The angular distribution parameterβ varies from 2 to −1 in an autoionization resonance belonging to the configuration ...(3d)9(4s)24p.