An experimental and computational study of the valence photoelectron spectra of halogenated pyrimidines

Abstract

The electronic structures of pyrimidine and a selection of its halogen-substituted derivatives have been investigated using ultraviolet photoelectron spectroscopy and ab initio quantum chemical methods. Assignments are proposed for all of the features in the PES spectra by comparison with the vertical ionization energies of the molecular orbitals calculated using the partial third-order quasiparticle approximation as applied to electron propagator theory and a corrected density functional method based on the B3LYP functional. The shifts of the outermost five molecular orbitals of the pyrimidine ring structure in the halogen-substituted derivatives with respect to the binding energies of the equivalent orbitals in the parent pyrimidine molecule are discussed as a function of the identity and ring position of the halogen atom.

Keywords:

• photoelectron spectra
• halogenated pyrimidines
• substituent effects
• density functional theory
• electron propagator theory

Acknowledgements

The authors are grateful for the technical help provided by Dr. Ettore Fainelli and Marcello Mastropietro. The authors would also like to thank the High Performance Computing center at CINECA for computing time awarded via the Progetto Supercalcolo Convenzione CINECA-INFM-CNR.