Shake-up phenomena in D +ArA − structures: A CNDO/S equivalent-core study on N,N-dimethyl- p-nitroaniline in the vapor and condensed phases

Abstract

The nature and manifestations of perturbations to the valence orbital manifold of N,N-dimethyl- p-nitroaniline (DMPNA) in the vapor and condensed phases due to appropriate core-hole states and addressed within the equivalent-core approximation using the CNDO/S molecular orbital method. It is found that the doublet structures observed in the experimental solid phase XPS spectrum arising from N1s(NO 2) and O1s ionization can be resolved in terms of intense shake-up excitations calculated to accompany creation of the appropriate core-hole. Furthermore, we find that the differences resolved in the gas and solid phase XPS spectra of p-nitroaniline, for example, for both O1s and N1s signals reflect both crystal polarization energies, and orbital mixing effects, and that modifications to the N1s(NO 2) peak structure arising from the polar crystal environment are not inconsistent with an interpretation based on negative shake-up energies.