CONSISTENT ASSIGNMENT OF THE VIBRATIONS OF PARA DISUBSTITUTED BENZENE MOLECULES

When disubstituted benzene molecules are considered the relative position of the substituents must be defined. The three possible forms are ortho-, meta-, and parawhere the latter is investigated in this work by consideration of the effect para positioned substituents will have on the vibrational modes. The consistency of the labelling and assignment of the vibrational frequencies of the para disubstituted benzene molecules is investigated in their ground states (S0) and first electronically excited states (S1). The work extends a previously published nomenclature where ring-localised vibrations are compared straightforwardly across different monosubstituted benzene species and given the label Mi. The assignments of the frequencies include previous work but also the calculated wavenumbers for both hydrogenated disubstituted benzenes (-h4) and the deuterated isotopologues (-d4) employing density functional theory (DFT) and time-dependent density functional theory (TDDFT).