Theoretical and experimental studies of vibrational spectra of naphthalene and its cation

Raman and FTIR spectra of naphthalene and its cation have been systematically analyzed using ab-initio and density functional theory calculations. The optimized geometries, harmonic vibrational wave numbers and intensity of vibrational bands of naphthalene and its cation were calculated invoking different basis sets up to HF/6-311++G** and B3LYP/6311++G** level. Vibrational assignments have been made and calculated DFT frequencies and intensities of the naphthalene and its cation at B3LYP/6-311++G** levels and are found to be in better agreement with corresponding experimental values in comparison to previous results. The experimental and theoretical studies of neutral and ionized naphthalene have revealed an unexpected effect of the ionization on the vibrational spectra that lead to a dramatic reduction in intensities of CH stretching modes and concurrently large increase in the intensities of ring CC stretching and CH bending vibrations.