MOLECULAR-STRUCTURE AND INFRARED-SPECTRA OF FURAN, THIOPHENE, SELENOPHENE AND THEIR 2,5-N AND 3,4-N DERIVATIVES - DENSITY-FUNCTIONAL THEORYAND CONVENTIONAL POST-HARTREE-FOCK MP2 STUDIES

Molecular parameters (bond lengths and bond angles, rotational constan ts, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of furan, thiophene, selenophene and their 2,5-N and 3,4-N derivatives have been predicted by density functional theor y with the combined Becke3-LYP gradient exchange-corrected functional (DFT(B3LYP)) and the conventional ab initio MP2(full) approach. The st andard 6-31G(d,p) basis set was used for all atoms except selenium for which a partially uncontracted Huzinaga basis set supplemented with a set of d-polarization functions was employed. Results are compared wi th the available experimental data. The molecular parameters computed by means of the DFT method are in a good agreement with those predicte d by the MP2 approach and with the experimental data. The calculated d ata suggest verification of the experimental data for the bond angles of selenophene. Very good agreement between the calculated IR wavenumb ers and absorption IR intensities of the molecules studied and their d euterated species by the DFT method and the experimental data was foun d. (C) 1997 Elsevier Science B.V.