Calculations of NEXAFS Spectra of Substituted Benzenes

We examine the role of substituent strengths and positions for NEXAFS spectra of substituted benzenes by means of static exchange calculations on aniline, phenol, fluorobenzene, and terephthalaldehyde. Chemical shifts and intensities of the 1s → π* excitations are found to be closely related to the electronegative character of the substituent group. The intensities for the unconnected ring carbons exhibit a significant site dependent, alternant, behaviour, while the chemical shifts in the energy positions are small. The terephthalaldehyde molecule shows a crucial positional dependence for double substitution and gives also a nice example of the building block principle for NEXAFS. New assignments are given for the building blocks in the terephthalaldehyde spectrum and for all salient features in the discrete parts of the monosubstituted benzene spectra