Ab initio and DFT investigations for the isatin dimer

Theoretical investigations on the geometric and energetic properties, rotational constants, harmonic vibrational frequencies and IR intensities, of isatin monomer and dimer are carried out by using the density functional theory and MP2 calculations. The binding energy of the isatin dimer was found to be 15.35 kcal/mol (with BSSE correction) at MP2/6-31G (d,p) level, indicating relatively a strong heteronuclear hydrogen bonding, NH center dot center dot center dot O=C, between the isatin monomers. The calculated vertical excitation energies for valence excited (singlet) states are in consonance to the experimental absorption peaks. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.