High-resolution electron momentum spectroscopy of molecules

We report on the application of electron momentum spectroscopy to the chemically interesting molecules [1.1.1]propellane, cubane and norbornadiene. Detailed binding energy spectra and orbital momentum distributions (MDs) were measured. This work, particululy for the larger molecules C8H8 (cubane) and C7H8 (norbornadiene), was made feasible by the development at Flinders of an (e,2e) monochromator, so that our coincidence energy resolution improved from typically 1.4 eV (FWHM) to about 0.5 eV (FWHM). In conjunction with these experiments we utilise the UniChem computational chemistry codes and the Flinders-developed AMOLD program to calculate theoretical MDs for each orbital of each species. A critical comparison between the experimental and theoretical MDs enabled us to determine, for a given molecule, the optimum basis set from those we studied. The determination of this basis set then allowed us to make further use of the UniChem package to derive each molecule's molecular properties and, in particular, address open questions as to the nature of the bonding in [1.1.1]propellane, cubane and norbornadiene.