Ionization potentials of nitriles — Photoelectron spectra of succinonitrile and glutaronitrile

Abstract

The He(I) photoelectron spectra of succinonitrile (1) and glutaronitrile (2), both with extensive overlap of ionization bands in the low-energy region, are reported. To assign ionizations, we studied the conformational behaviour and resulting ionization energy dependence of 1 and 2 computationally with the B3LYP/6-31+G(d) model chemistry based on the fact that it reliably reproduces the ionization potentials of eleven mono- and di-nitriles, both saturated and unsaturated. The correlation of proton affinities with observed ionization potentials of 1, 2, and malononitrile establishes the orbital sequence of four C≡N π orbitals followed by two nitrogen lone pair orbitals as the highest occupied molecular orbitals for all three compounds.Key words: photoelectron spectrum, ionization potential, conformational dependence, nitrile, DFT.