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Dedicated to Edgar Heilbronner on the occasion of his 80th birthdayThe electronic structure of spiro [4.4]nonatetraene 1 as well as that of its radical anion and cation were studied by different spectroscopies. The electron-energy-loss spectrum in the gas phase revealed the lowest triplet state at 2.98 eV and a group of three overlapping triplet states in the 4.5 ± 5.0 eV range, as well as a number of valence and Rydberg singlet excited states. Electron-impact excitation functions of pure vibrational and triplet states identified various states of the negative ion, in particular the ground state with an attachment energy of 0.8 eV, an excited state corresponding to a temporary electron attachment to the 2b 1 MO at an attachment energy of 2.7 eV, and a core excited state at 4.0 eV. Electronic-absorption spectroscopy in cryogenic matrices revealed several states of the positive ion, in particular a richly structured first band at 1.27 eV, and the first electronic transition of the radical anion. Vibrations of the ground state of the cation were probed by IR spectroscopy in a cryogenic matrix. The results are discussed on the basis of density-functional and CASSCF/ CASPT2 quantum-chemical calculations. In their various forms, the calculations successfully rationalized the triplet and the singlet (valence and Rydberg) excitation energies of the neutral molecule, the excitation energies of the radical cation, its IR spectrum, the vibrations excited in the first electronic absorption band, and the energies of the ground and the first excited states of the anion. The difference of the anion excitation energies in the gas and condensed phases was rationalized by a calculation of the Jahn-Teller distortion of the anion ground state. Contrary to expectations based on a single-configuration model for the electronic states of 1, it is found that the gap between the first two excited states is different in the singlet and the triplet manifold. This finding can be traced to the different importance of configuration interaction in the two multiplicity manifolds.1. Introduction. ± Spiroconjugation, a concept first introduced in 1967 [1] [2], results in many interesting spectroscopic and chemical properties. As a consequence, spiroconjugated compounds have often been studied experimentally and theoretically, and they find applications in technology (e.g., as materials for organic light-emitting diodes [3] or nonlinear optical materials).

Electron-induced chemistry-dissociative electron attachment (DEA)-was studied for phenyl azide. The major fragment corresponded to the loss of N 2 and formation of the phenylnitrene anion. This process has an onset already at zero kinetic energy of the incident electron and is interpreted as proceeding via the A π * electronic ground state of the phenyl azide anion. Other fragments, N − 3 and CN − , were observed at higher energies and interpreted as proceeding via low-lying shape resonances or higher lying core-excited resonances. The interpretation of the dissociative attachment spectra was supported by an investigation of the excited electronic states of neutral phenyl azide by electron energy-loss spectroscopy and DFT/MRCI calculations, and a study of shape and core-excited resonances of the phenyl azide anion by means of electron transmission spectroscopy and of cross sections for vibrational and electronic excitation by electron impact. Interesting parallels and differences are found by comparing DEA of phenyl and benzyl azides with the corresponding chloro compounds.