Ground and first electronic excited state vibrational modes of the methyl-p-aminobenzoate molecule

Laser induced fluorescence, dispersed emission and two-colour ionisation spectroscopy (including the ionisation energy threshold) are suggested as an appropriate set of experimental methods for drawing the ground and excited state vibrational spectra of large organic molecules in presence of solvated molecules and dimers. In this Letter, they have been applied to obtain the vibrational spectrum of methyl-p-aminobenzoate (MAB). Parallel ground state ab initio calculations have enabled the geometry to be determined and the vibrational modes to be accurately assigned. The comparison of the ground and the first electronic excited state vibrational band wavenumbers shows an excellent agreement except for the excited state bands observed at 52.2, 565.6 and 579.7 cm−1.