Search

Photoelectron-photoion coincidence measurements on the methyl halide ion dissociations show that when these ions are formed in different electronic states they undergo specific reactions to different products. Some interconversion between electronic states also occurs to an extent which correlates with the energy gaps between the states concerned. Within certain states the vibrational energy is not statistically redistributed before fragmentation.

Branching ratios for fragmentation to different products and kinetic energies released in dissociation have been measured as functions of the internal energy of the parent ions of propane and neopentane using the photoelectronphotoion coincidence technique. The results affirm the statistical fragmentation model for propane ions and suggest it in the case of neopentane ions.

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.

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.

Carbon disulphide ions initially produced by photoionization in the C (2Σg+) and D (2Σu+) states are shown to decompose to all the energetically possible products, and branching ratios for the different processes are given. The kinetic energy release distributions for the five fragmentations have also been measured. The results are discussed in terms of rapid internal conversion processes preceding predissociation.

Photoelectron spectra measured with 21.22 eV and 12.08 eV light are used to determine the contribution of autoionization processes to the photoionization cross sections of methanol and ethanol. The most important of fragmentation processes of the molecular ions are investigated using the technique of measuring photoelectron spectra in coincidence with mass-analysed ions. It is shown that some structures observed in the photoionization cross sections of these molecules are due to autoionization processes rather than to isolated electronic states of the ions.