The authors report absolute differential and integral cross section measurements for electron-impact excitation of the ÃB11 electronic state of water. This is an important channel for the production of the OH (X̃Π2) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20–200eV, while the angular range of the differential cross section data is 3.5°–90°. This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment.

Momentum Distributions (MDs), obtained using high-resolution electron momentum spectroscopy (HREMS), are reported for norbornadiene's 18 valence orbitals. Corresponding theoretical results, using generalized gradient approximation density functional theory (DFT) together with TZVP, DZVP, and DZVP2 basis functions and a plane wave impulse approximation to describe the ionization process, are also detailed. This work represents the first comprehensive HREMS/DFT investigation into the complete valence electronic structure of norbornadiene (NBD), with significant results being obtained. In particular, an exacting comparison between our experimental and theoretical MDs enables us to define the “optimum” basis for NBD, from those we studied. This “optimum” basis is then used to extract a wide range of NBD's important molecular property information, which are subsequently compared with the results of independent measurements and calculations. Agreement between our results and those from independent measurements was generally very good, highlighting the utility of HREMS in a priori basis set evaluation.