The suitability of density functional (DFT) methods for an accurate determination of ionization potentials is the object of a systematic analysis. The studied systems are unsaturated molecules containing 14 and 15 main group elements. The results, which have involved five different functionals, are compared to experimental results and to values estimated from calculations performed at the Møller-Plesset level up to second order.

The coupling of flash vacuum thermolysis reactions (retro [2+2] cleavages) with photoelectron spectroscopy allowed the first direct characterization of several highly reactive N-alkylated silanimines. For the trimethylsilanimine 1b, the IPs corresponding to the ejection of an electron from the nitrogen lone pair (n(N)) and the pi(Si)(=)(N) orbital are observed at 7.9 and 8.3 eV, respectively. In the case of the N-isopropylated and N-tert-butylated analogues 1c,d, these characteristic ionizations are energetically closed (7.8 and 7.4 eV). These unexpected attributions have been corroborated by the ab initiocalculations of the ionization energies using 6-31G(d) and LANL1DZ basis sets and MP2 level. Our results have been completed by the determination of the structural and electronic characteristics of these silanimines.