Vibrational analysis of the spectra of furan and thiophene

Scaled-quantum-mechanical (SQM) force fields were calculated for furan and thiophene, and their isotopomers, at the B3LYP, MP2 and HF levels of theory using the 6-31G** basis set. With the exception of few bands, mainly for the C-H (C-D) stretching mode, an excellent agreement between the calculated and experimental frequencies is obtained. The agreement between the calculated and experimental IR absorption intensities was satisfactory except at the MP2 level where the agreement was poorer than expected. The B3LYP scale factors are better correlated and less divergent than those obtained by the MP2 or the HF force fields. The B3LYP scale factors are also in good agreement with those previously reported. (C) 1997 Elsevier Science B.V.