TDDFT studies for electronic excitations of the intermediates and radicals in the pyrolysis of 2,5-dimethylfuran

A large amount of complicated reaction networks of intermediates and radicals taken place in the pyrolysis of 2,5-dimethylfuran have been investigated based on the density function theory (DFT) and the sophisticated wave function theory (WFT) methodologies. The preliminary focus is concentrated on those without the furan-ring opening reaction processes. Calculations are performed for electronic structures, stability and electronic spectra of ground states and excited states for those intermediates and radicals. It is found that both low-lying valence excited states and Rydberg states (3s, 3p_x, 3p_y and 3p_z) of the pyrolytic species might be involved in pyrolysis and combustion of 2,5-dimethylfuran and influence their chemical reaction kinetics. A generous tendency is also found that the vertical transition energies of the similar transitions become bigger with the removal of methyl in the furan ring.