Protonation Effects on the Electronic Spectra of Pyrazine

Abstract

Abstract The protonation effect on the electronic structure and spectra of pyrazine has been studied theoretically employing quantum mechanical calculation. Semi-empirical Hartree-Fock SCF MO’s for pyrazine interacting with two protons have been computed with two different methods, respectively. i) Electrostatic potential due to proton has been added to the core potential in the total electronic Hamiltonian and nuclear attraction integrals which arise owing to the proton potential have been computed theoretically employing the usual Slater 2pπ AO’s. ii) The doubly protonated pyrazine has been replaced by doubly charged pyrazinium ion and molecular integrals have been evaluated semi-empirically using valence state ionization potential and electron affinity of the N+ atom. The calculated spectra with method i are in a very good agreement with the experiment. The calculation with method ii has led to a result which is in rather poor agreement with the experimental observation. On the basis of these results, some discussions about the protonation effect on the electronic structure of this molecule have been given.