ESCA and UPS Spectra of Nitronaphthylamines. Shake-up structures, relaxation effects and through-space interaction between the two substituents

Abstract

The X-ray and UV photoelectron spectra of several nitronaphthylamine isomers are reported. In some cases, the nitro N_1s signal is accompanied by an intense satellite band 1.5-2.0 eV from the main photoline having 60-150% of its intensity; also in the corresponding O_1s energy region a satellite band is present having a larger energy separation from the main peak (2.0-2.3₅ eV) and smaller relative intensity (I _sh = 10-30%). The difference between the ionization energy values of the nitro and amino N_1s signal (ΔN_1s ) is found to follow the same trend found for the intensity of the satellite and log ϵ, the optical absorption coefficient of the HOMO-LUMO charge-transfer (CT) transition. These satellites are ascribed to a shake-up process involving a CT transition from the naphthylamine part of the molecule towards a π* MO localized on the nitro group on the basis of a simple model we have previously proposed for nitroanilines and other aromatic derivatives. The trend of ΔN_1s is thought to derive mainly from a greater "interatomic" valence band relaxation accompanying nitro N_1s ionization than amino N_1s ionization, rather than from variation of the ground state charges at the two nitrogen atoms. The UPS spectra indicate that there is no sizeable variation of the ground state mesomeric interaction between the two substituents on changing the position of the nitro group, and suggest mutual interaction of the two substituents when they are adjacent.