THEORETICAL AND EXPERIMENTAL-DETERMINATION OF THE ELECTRONIC-SPECTRUM OF NORBORNADIENE

The electronic spectrum of the nonplanar, indirectly conjugated molecule norbornadiene has been studied theoretically, using multiconfigurational second-order perturbation theory (CASPT2) with extended ANO-type basis sets, and experimentally, using optical absorption and polarization-selected two-photon resonant-enhanced multiphoton ionization (REMPI) spectroscopies. The calculations comprise five valence excited states and the 3s, 3p, and 3d members of the Rydberg series converging on the first two ionizations. The two lowest triplet states have also been studied. The experiments enabled definitive assignments to be made for four Rydberg transitions and three valence transitions. The computed excitation energies were found to be within 0.2 eV of the experimental energies for correctly correlated transitions; the computed oscillator strengths were in good relative: agreement with their experimental values. Comparisons are made between this and other theoretical calculations and also between the electronic spectra of norbornadiene, cis-butadiene, and cyclopentadiene.