Vibrational Spectra (FT-IR, FT-Raman), NBO and HOMO, LUMO Studies of 2-Thiophene Carboxylic Acid Based On Density Functional Method.

Abstract

The molecular structure and vibrational spectra of 2-thiophene carboxylic acid (TCA) is calculated with the help of B3LYP density functional theory (DFT) using 6-31G** as basis set. The solid phase FTIR and FT-Raman spectra of TCA have been recorded in the range 4000 - 400 and 3500-50 cm -1 respectively. On the basis of B3LYP calculations, the normal coordinate analysis is performed to assign the vibrational fundamental frequencies according to potential energy distribution (PED). The over estimations of the calculated wave numbers are corrected by the aid of scaled quantum mechanical force field methodology (SQMFF). The computational frequencies are in good agreement with the observed results. The stability of the molecule is analyzed using NBO analysis.The calculated HOMO and LUMO energies show that charge transfer that charge transfer occurs within the molecule. Keywords - TCA,FTIR, FT-Raman, DFT, NBO.