Studies have been made of the two outgoing electrons in ionization events for which the energy difference E between the total energy and the ionization energy is in the range from 0.2 to 3.0 eV. A coincidence time-of-flight technique has been used to measure their energy distribution and angular correlation functions, and a non-coincidence technique has been used to measure the partial cross section for the production of very slow electrons. The energy distribution function has been found to be uniform in the range of E from 0.2 to 0.8 eV and the width of the angular correlation function has been found to increase with the energy E in a way which is consistent with a E l l 4 dependence. The yield of very low energy electrons is consistent, in the range of E from 0.2 to 1.7 eV, with a total ionization cross section having the energy dependence E", where n = 1,131 +0.019. These results are all consistent with the Wannier-PeterkopRau theory.

Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction ('gerade' and 'ungerade') are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N(2) through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species--a phenomenon analogous to the acquisition of partial 'which-way' information in macroscopic double-slit experiments.

For emission out of the molecule along the molecular axis, the direct wave interferes with an electron wave that is scattered an odd number of times and dominated by singlescattering (66% back-scattering), whereas for emission into the molecule, the direct