ab initio calculations have been performed using quantum chemical method to compute optimized geometries, atomic charges, harmonic vibrational frequencies along with intensities in IR and Raman spectra and depolarization ratios of the Raman bands for the 1,4-Naphthoquinone (NQ) and 2-Methyl-1,4-Naphthoquinone (MNQ) and their corresponding radical anions (NQ-and MNQ-) species. Most of the vibrational frequencies have nearly the same magnitude for the NQ, MNQ and their radical anions; however,

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... nificant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands. For the neutral NQ molecule and its radical anions, the magnitude of the atomic charges at the atoms C 1 and C 4 are almost identical and possess more positive charge due to the attachment of O atom at the sites C 1 and C 4. But in the case of MNQ and its radical anions are found to be not identical due to the electron withdrawing nature of CH 3 group attached at the sites C 2. The present calculations predict that the thermodynamical stability order based on the total energy E increases in the following orders: NQ->NQ and MNQ->MNQ, thus, anionic form is more stable as compared to their neutral form. The magnitude of zero-point vibrational energy (ZPVE) and thermal energy correction (E) decreases slightly in going from NA to NA-(by 4.127/3.609), NQ to NQ-(by 1.396/1.492) and MNQ to MNQ-(by 2.536/1.569) (in Kcal/Mol) respectively.